--- a/addon-sdk/source/lib/sdk/addon/runner.js
+++ b/addon-sdk/source/lib/sdk/addon/runner.js
@@ -65,28 +65,28 @@ function startup(reason, options) {
 
     // NOTE: Module is intentionally required only now because it relies
     // on existence of hidden window, which does not exists until startup.
     let { ready } = require('../addon/window');
     // Load localization manifest and .properties files.
     // Run the addon even in case of error (best effort approach)
     require('../l10n/loader').
       load(rootURI).
-      then(null, function failure(error) {
+      catch(function failure(error) {
         if (!isNative)
           console.info("Error while loading localization: " + error.message);
       }).
       then(function onLocalizationReady(data) {
         // Exports data to a pseudo module so that api-utils/l10n/core
         // can get access to it
         definePseudo(options.loader, '@l10n/data', data ? data : null);
         return ready;
       }).then(function() {
         run(options);
-      }).then(null, console.exception);
+      }).catch(console.exception);
     return void 0; // otherwise we raise a warning, see bug 910304
   });
 }
 
 function run(options) {
   try {
     // Try initializing HTML localization before running main module. Just print
     // an exception in case of error, instead of preventing addon to be run.

--- a/addon-sdk/source/lib/sdk/l10n/loader.js
+++ b/addon-sdk/source/lib/sdk/l10n/loader.js
@@ -10,17 +10,17 @@ module.metadata = {
 const { Cc, Ci } = require("chrome");
 lazyRequire(this, "./locale", "getPreferedLocales", "findClosestLocale");
 lazyRequire(this, "../net/url", "readURI");
 lazyRequire(this, "../core/promise", "resolve");
 
 function parseJsonURI(uri) {
   return readURI(uri).
     then(JSON.parse).
-    then(null, function (error) {
+    catch(function (error) {
       throw Error("Failed to parse locale file:\n" + uri + "\n" + error);
     });
 }
 
 // Returns the array stored in `locales.json` manifest that list available
 // locales files
 function getAvailableLocales(rootURI) {
   let uri = rootURI + "locales.json";

--- a/addon-sdk/source/test/addons/page-mod-debugger-post/main.js
+++ b/addon-sdk/source/test/addons/page-mod-debugger-post/main.js
@@ -38,17 +38,17 @@ exports.testDebugger = function(assert, 
           then(_ => { assert.pass('attachTabActorForUrl called'); return _; }).
           then(attachThread).
           then(testDebuggerStatement).
           then(_ => { assert.pass('testDebuggerStatement called') }).
           then(closeConnection).
           then(_ => { assert.pass('closeConnection called') }).
           then(_ => { tab.close() }).
           then(done).
-          then(null, aError => {
+          catch(aError => {
             ok(false, "Got an error: " + aError.message + "\n" + aError.stack);
           });
       }
     });
   });
 }
 
 function attachThread([aGrip, aResponse]) {

--- a/addon-sdk/source/test/addons/page-mod-debugger-pre/main.js
+++ b/addon-sdk/source/test/addons/page-mod-debugger-pre/main.js
@@ -45,17 +45,17 @@ exports.testDebugger = function(assert, 
           then(_ => { assert.pass('attachTabActorForUrl called'); return _; }).
           then(attachThread).
           then(testDebuggerStatement).
           then(_ => { assert.pass('testDebuggerStatement called') }).
           then(closeConnection).
           then(_ => { assert.pass('closeConnection called') }).
           then(_ => { tab.close() }).
           then(done).
-          then(null, aError => {
+          catch(aError => {
             ok(false, "Got an error: " + aError.message + "\n" + aError.stack);
           });
       }
     });
   });
 }
 
 function attachThread([aGrip, aResponse]) {

--- a/addon-sdk/source/test/addons/places/lib/test-places-host.js
+++ b/addon-sdk/source/test/addons/places/lib/test-places-host.js
@@ -61,17 +61,17 @@ exports.testBookmarksCreateFail = functi
     type: 'bookmark'
   }, {
     type: 'group',
     group: bmsrv.bookmarksMenuFolder
   }, {
     group: bmsrv.unfiledBookmarksFolder
   }];
   all(items.map(function (item) {
-    return send('sdk-places-bookmarks-create', item).then(null, function (reason) {
+    return send('sdk-places-bookmarks-create', item).catch(function (reason) {
       assert.ok(reason, 'bookmark create should fail');
     });
   })).then(done);
 };
 
 exports.testBookmarkLastUpdated = function (assert, done) {
   let timestamp;
   let item;

--- a/addon-sdk/source/test/addons/private-browsing-supported/test-selection.js
+++ b/addon-sdk/source/test/addons/private-browsing-supported/test-selection.js
@@ -228,24 +228,24 @@ exports["test PWPB Selection Listener"] 
           assert.ok(isFocused(window), "the window is focused");
           assert.ok(isPrivate(window), "the window should be a private window");
 
           assert.equal(selection.text, "fo");
 
           closeWindow(window).
             then(loader.unload).
             then(done).
-            then(null, assert.fail);
+            catch(assert.fail);
         });
       });
       return window;
     }).
     then(selectContentFirstDiv).
     then(dispatchSelectionEvent).
-    then(null, assert.fail);
+    catch(assert.fail);
 };
 
 exports["test PWPB Textarea OnSelect Listener"] = function(assert, done) {
   let loader = Loader(module);
   let selection = loader.require("sdk/selection");
 
   open(URL, {private: true, title: "PWPB OnSelect Listener"}).
     then(function(window) {
@@ -258,24 +258,24 @@ exports["test PWPB Textarea OnSelect Lis
 
         // window should be focused, but force the focus anyhow.. see bug 841823
         focus(window).then(function() {
           assert.equal(selection.text, "noodles");
 
           closeWindow(window).
             then(loader.unload).
             then(done).
-            then(null, assert.fail);
+            catch(assert.fail);
         });
       });
       return window;
     }).
     then(selectTextarea).
     then(dispatchOnSelectEvent).
-    then(null, assert.fail);
+    catch(assert.fail);
 };
 
 exports["test PWPB Single DOM Selection"] = function(assert, done) {
   let loader = Loader(module);
   let selection = loader.require("sdk/selection");
 
   open(URL, {private: true, title: "PWPB Single DOM Selection"}).
     then(selectFirstDiv).
@@ -299,17 +299,17 @@ exports["test PWPB Single DOM Selection"
         assert.equal(sel.html, "<div>foo</div>",
           "iterable selection.html with single DOM Selection works.");
       }
 
       assert.equal(selectionCount, 1,
         "One iterable selection");
 
       return closeWindow(window);
-    }).then(loader.unload).then(done).then(null, assert.fail);
+    }).then(loader.unload).then(done).catch(assert.fail);
 }
 
 exports["test PWPB Textarea Selection"] = function(assert, done) {
   let loader = Loader(module);
   let selection = loader.require("sdk/selection");
 
   open(URL, {private: true, title: "PWPB Textarea Listener"}).
     then(selectTextarea).
@@ -335,17 +335,17 @@ exports["test PWPB Textarea Selection"] 
         assert.strictEqual(sel.html, null,
           "iterable selection.html with Textarea Selection works.");
       }
 
       assert.equal(selectionCount, 1,
         "One iterable selection");
 
       return closeWindow(window);
-    }).then(loader.unload).then(done).then(null, assert.fail);
+    }).then(loader.unload).then(done).catch(assert.fail);
 };
 
 exports["test PWPB Set HTML in Multiple DOM Selection"] = function(assert, done) {
   let loader = Loader(module);
   let selection = loader.require("sdk/selection");
 
   open(URL, {private: true, title: "PWPB Set HTML in Multiple DOM Selection"}).
     then(selectAllDivs).
@@ -375,17 +375,17 @@ exports["test PWPB Set HTML in Multiple 
 
         selectionCount++;
       }
 
       assert.equal(selectionCount, 2,
         "Two iterable selections");
 
       return closeWindow(window);
-    }).then(loader.unload).then(done).then(null, assert.fail);
+    }).then(loader.unload).then(done).catch(assert.fail);
 };
 
 exports["test PWPB Set Text in Textarea Selection"] = function(assert, done) {
   let loader = Loader(module);
   let selection = loader.require("sdk/selection");
 
   open(URL, {private: true, title: "test PWPB Set Text in Textarea Selection"}).
     then(selectTextarea).
@@ -412,17 +412,17 @@ exports["test PWPB Set Text in Textarea 
         assert.strictEqual(sel.html, null,
           "iterable selection.html with Textarea Selection works.");
       }
 
       assert.equal(selectionCount, 1,
         "One iterable selection");
 
       return closeWindow(window);
-    }).then(loader.unload).then(done).then(null, assert.fail);
+    }).then(loader.unload).then(done).catch(assert.fail);
 };
 
 // If the platform doesn't support the PBPW, we're replacing PBPW tests
 if (!require("sdk/private-browsing/utils").isWindowPBSupported) {
   module.exports = {
     "test PBPW Unsupported": function Unsupported (assert) {
       assert.pass("Private Window Per Browsing is not supported on this platform.");
     }

--- a/addon-sdk/source/test/addons/private-browsing-supported/test-sidebar.js
+++ b/addon-sdk/source/test/addons/private-browsing-supported/test-sidebar.js
@@ -35,17 +35,17 @@ exports.testSideBarIsInNewPrivateWindows
       assert.ok(isPrivate(window), 'the new window is private');
       assert.ok(!!ele, 'sidebar element was added');
 
       sidebar.destroy();
       assert.ok(!window.document.getElementById(makeID(testName)), 'sidebar id DNE');
       assert.ok(!startWindow.document.getElementById(makeID(testName)), 'sidebar id DNE');
 
       return close(window);
-  }).then(done).then(null, assert.fail);
+  }).then(done).catch(assert.fail);
 }
 
 // Disabled in order to land other fixes, see bug 910647 for further details.
 /*
 exports.testSidebarIsOpenInNewPrivateWindow = function(assert, done) {
   const { Sidebar } = require('sdk/ui/sidebar');
   let testName = 'testSidebarIsOpenInNewPrivateWindow';
   let window = getMostRecentBrowserWindow();
@@ -137,18 +137,18 @@ exports.testDestroyEdgeCaseBugWithPrivat
           assert.equal(isSidebarShowing(window), false, 'the sidebar is not showing');
 
           done();
         }
       })
 
       sidebar.show();
       assert.pass('showing the sidebar');
-    }).then(null, assert.fail);
-  }).then(null, assert.fail);
+    }).catch(assert.fail);
+  }).catch(assert.fail);
 }
 
 exports.testShowInPrivateWindow = function(assert, done) {
   const { Sidebar } = require('sdk/ui/sidebar');
   let testName = 'testShowInPrivateWindow';
   let window1 = getMostRecentBrowserWindow();
   let url = 'data:text/html;charset=utf-8,'+testName;
 
@@ -183,22 +183,22 @@ exports.testShowInPrivateWindow = functi
                   'the menuitem on the new window dne');
 
         // test old window state
         assert.equal(isSidebarShowing(window1), false, 'the old window sidebar is not showing');
         assert.equal(window1.document.getElementById(menuitemID),
                      null,
                      'the menuitem on the old window dne');
 
-        close(window).then(done).then(null, assert.fail);
+        close(window).then(done).catch(assert.fail);
       },
       function bad() {
         assert.fail('a successful show should not happen here..');
       });
-  }).then(null, assert.fail);
+  }).catch(assert.fail);
 }
 
 // If the module doesn't support the app we're being run in, require() will
 // throw.  In that case, remove all tests above from exports, and add one dummy
 // test that passes.
 try {
   require('sdk/ui/sidebar');
 }

--- a/addon-sdk/source/test/addons/private-browsing-supported/test-window-tabs.js
+++ b/addon-sdk/source/test/addons/private-browsing-supported/test-window-tabs.js
@@ -13,63 +13,63 @@ exports.testOpenTabWithPrivateActiveWind
 
   windowPromise(window, 'load').then(focus).then(function (window) {
     assert.ok(isPrivate(window), 'new window is private');
 
     tabs.open({
       url: 'about:blank',
       onOpen: function(tab) {
         assert.ok(isPrivate(tab), 'new tab is private');
-        close(window).then(done).then(null, assert.fail);
+        close(window).then(done).catch(assert.fail);
       }
     })
-  }).then(null, assert.fail);
+  }).catch(assert.fail);
 }
 
 exports.testOpenTabWithNonPrivateActiveWindowNoIsPrivateOption = function(assert, done) {
   let window = getMostRecentBrowserWindow().OpenBrowserWindow({ private: false });
 
   windowPromise(window, 'load').then(focus).then(function (window) {
     assert.equal(isPrivate(window), false, 'new window is not private');
 
     tabs.open({
       url: 'about:blank',
       onOpen: function(tab) {
         assert.equal(isPrivate(tab), false, 'new tab is not private');
-        close(window).then(done).then(null, assert.fail);
+        close(window).then(done).catch(assert.fail);
       }
     })
-  }).then(null, assert.fail);
+  }).catch(assert.fail);
 }
 
 exports.testOpenTabWithPrivateActiveWindowWithIsPrivateOptionTrue = function(assert, done) {
   let window = getMostRecentBrowserWindow().OpenBrowserWindow({ private: true });
 
   windowPromise(window, 'load').then(focus).then(function (window) {
     assert.ok(isPrivate(window), 'new window is private');
 
     tabs.open({
       url: 'about:blank',
       isPrivate: true,
       onOpen: function(tab) {
         assert.ok(isPrivate(tab), 'new tab is private');
-        close(window).then(done).then(null, assert.fail);
+        close(window).then(done).catch(assert.fail);
       }
     })
-  }).then(null, assert.fail);
+  }).catch(assert.fail);
 }
 
 exports.testOpenTabWithNonPrivateActiveWindowWithIsPrivateOptionFalse = function(assert, done) {
   let window = getMostRecentBrowserWindow().OpenBrowserWindow({ private: false });
 
   windowPromise(window, 'load').then(focus).then(function (window) {
     assert.equal(isPrivate(window), false, 'new window is not private');
 
     tabs.open({
       url: 'about:blank',
       isPrivate: false,
       onOpen: function(tab) {
         assert.equal(isPrivate(tab), false, 'new tab is not private');
-        close(window).then(done).then(null, assert.fail);
+        close(window).then(done).catch(assert.fail);
       }
     })
-  }).then(null, assert.fail);
+  }).catch(assert.fail);
 }

--- a/addon-sdk/source/test/addons/private-browsing-supported/test-windows.js
+++ b/addon-sdk/source/test/addons/private-browsing-supported/test-windows.js
@@ -69,17 +69,17 @@ exports.testWindowTrackerIgnoresPrivateW
       assert.pass('private window was closed');
 
       return makeEmptyBrowserWindow().then(function(window) {
         myNonPrivateWindowId = getInnerId(window);
         assert.notEqual(myPrivateWindowId, myNonPrivateWindowId, 'non private window was opened');
         return close(window);
       });
     });
-  }).then(null, assert.fail);
+  }).catch(assert.fail);
 };
 
 // Test setting activeWIndow and onFocus for private windows
 exports.testSettingActiveWindowDoesNotIgnorePrivateWindow = function(assert, done) {
   let browserWindow = WM.getMostRecentWindow("navigator:browser");
   let testSteps;
 
   assert.equal(winUtils.activeBrowserWindow, browserWindow,
@@ -141,17 +141,17 @@ exports.testSettingActiveWindowDoesNotIg
         continueAfterFocus(winUtils.activeWindow = browserWindow);
       },
       function() {
         assert.strictEqual(winUtils.activeBrowserWindow, browserWindow,
                           "Correct active browser window when pb mode is supported [4]");
         assert.strictEqual(winUtils.activeWindow, browserWindow,
                           "Correct active window when pb mode is supported [4]");
 
-        close(window).then(done).then(null, assert.fail);
+        close(window).then(done).catch(assert.fail);
       }
     ];
 
     function nextTest() {
       let args = arguments;
       if (testSteps.length) {
         require('sdk/timers').setTimeout(function() {
           (testSteps.shift()).apply(null, args);
@@ -231,10 +231,10 @@ exports.testWindowIteratorPrivateDefault
     assert.equal(isPrivate(winUtils.activeWindow), isWindowPBSupported);
     assert.equal(isPrivate(getMostRecentWindow()), isWindowPBSupported);
     assert.equal(isPrivate(browserWindows.activeWindow), isWindowPBSupported);
 
     assert.equal(browserWindows.length, 2, '2 windows open');
     assert.equal(windows(null, { includePrivate: true }).length, 2);
 
     return close(window);
-  }).then(done).then(null, assert.fail);
+  }).then(done).catch(assert.fail);
 };

--- a/addon-sdk/source/test/tabs/test-firefox-tabs.js
+++ b/addon-sdk/source/test/tabs/test-firefox-tabs.js
@@ -70,17 +70,17 @@ exports.testBrowserWindowCreationOnActiv
   tabs.once('activate', function onActivate(eventTab) {
     assert.ok(windows.activeWindow, "Is able to fetch activeWindow");
     gotActivate = true;
   });
 
   open().then(function(window) {
     assert.ok(gotActivate, "Received activate event");
     return close(window);
-  }).then(done).then(null, assert.fail);
+  }).then(done).catch(assert.fail);
 }
 
 // TEST: tab unloader
 exports.testAutomaticDestroyEventOpen = function(assert, done) {
   let called = false;
   let loader = Loader(module);
   let tabs2 = loader.require("sdk/tabs");
   tabs2.on('open', _ => called = true);
@@ -171,17 +171,17 @@ exports.testTabPropertiesInNewWindow = f
   });
 
   let tabs = loader.require('sdk/tabs');
   let { viewFor } = loader.require('sdk/view/core');
 
   let count = 0;
   function onReadyOrLoad (tab) {
     if (count++) {
-      close(getOwnerWindow(viewFor(tab))).then(done).then(null, assert.fail);
+      close(getOwnerWindow(viewFor(tab))).then(done).catch(assert.fail);
     }
   }
 
   let url = "data:text/html;charset=utf-8,<html><head><title>foo</title></head><body>foo</body></html>";
   tabs.open({
     inNewWindow: true,
     url: url,
     onReady: function(tab) {
@@ -264,17 +264,17 @@ exports.testTabContentTypeAndReload = fu
       url: url,
       onReady: function(tab) {
         if (tab.url === url) {
           assert.equal(tab.contentType, "text/html");
           tab.url = urlXML;
         }
         else {
           assert.equal(tab.contentType, "text/xml");
-          close(window).then(done).then(null, assert.fail);
+          close(window).then(done).catch(assert.fail);
         }
       }
     });
   });
 };
 
 // TEST: tabs iterator and length property
 exports.testTabsIteratorAndLength = function(assert, done) {
@@ -289,34 +289,34 @@ exports.testTabsIteratorAndLength = func
     tabs.open({
       url: url,
       onOpen: function(tab) {
         let count = 0;
         for (let t of tabs) count++;
         assert.equal(count, startCount + 3, "iterated tab count matches");
         assert.equal(startCount + 3, tabs.length, "iterated tab count matches length property");
 
-        close(window).then(done).then(null, assert.fail);
+        close(window).then(done).catch(assert.fail);
       }
     });
   });
 };
 
 // TEST: tab.url setter
 exports.testTabLocation = function(assert, done) {
   open().then(focus).then(function(window) {
     let url1 = "data:text/html;charset=utf-8,foo";
     let url2 = "data:text/html;charset=utf-8,bar";
 
     tabs.on('ready', function onReady(tab) {
       if (tab.url != url2)
         return;
       tabs.removeListener('ready', onReady);
       assert.pass("tab.load() loaded the correct url");
-      close(window).then(done).then(null, assert.fail);
+      close(window).then(done).catch(assert.fail);
     });
 
     tabs.open({
       url: url1,
       onOpen: function(tab) {
         tab.url = url2
       }
     });
@@ -360,20 +360,20 @@ exports.testTabMove = function(assert, d
     let url = "data:text/html;charset=utf-8,foo";
 
     tabs.open({
       url: url,
       onOpen: function(tab) {
         assert.equal(tab.index, 1, "tab index before move matches");
         tab.index = 0;
         assert.equal(tab.index, 0, "tab index after move matches");
-        close(window).then(done).then(null, assert.fail);
+        close(window).then(done).catch(assert.fail);
       }
     });
-  }).then(null, assert.fail);
+  }).catch(assert.fail);
 };
 
 exports.testIgnoreClosing = function*(assert) {
   let url = "data:text/html;charset=utf-8,foobar";
   let originalWindow = getMostRecentBrowserWindow();
 
   let window = yield open().then(focus);
 
@@ -476,17 +476,17 @@ exports.testOpenInNewWindow = function(a
 
       onFocus(newWindow).then(function() {
         assert.equal(getMostRecentBrowserWindow(), newWindow, "new window is active");
         assert.equal(tab.url, url, "URL of the new tab matches");
         assert.equal(newWindow.content.location, url, "URL of new tab in new window matches");
         assert.equal(tabs.activeTab.url, url, "URL of activeTab matches");
 
         return close(newWindow).then(done);
-      }).then(null, assert.fail);
+      }).catch(assert.fail);
     }
   });
 
 }
 
 // Test tab.open inNewWindow + onOpen combination
 exports.testOpenInNewWindowOnOpen = function(assert, done) {
   let startWindowCount = windows().length;
@@ -497,17 +497,17 @@ exports.testOpenInNewWindowOnOpen = func
     inNewWindow: true,
     onOpen: function(tab) {
       let newWindow = getOwnerWindow(viewFor(tab));
 
       onFocus(newWindow).then(function() {
         assert.equal(windows().length, startWindowCount + 1, "a new window was opened");
         assert.equal(getMostRecentBrowserWindow(), newWindow, "new window is active");
 
-        close(newWindow).then(done).then(null, assert.fail);
+        close(newWindow).then(done).catch(assert.fail);
       });
     }
   });
 };
 
 // TEST: onOpen event handler
 exports.testTabsEvent_onOpen = function(assert, done) {
   open().then(focus).then(window => {
@@ -520,21 +520,21 @@ exports.testTabsEvent_onOpen = function(
     };
     tabs.on('open', listener1);
 
     // add listener via collection add
     tabs.on('open', function listener2(tab) {
       assert.equal(++eventCount, 2, "both listeners notified");
       tabs.removeListener('open', listener1);
       tabs.removeListener('open', listener2);
-      close(window).then(done).then(null, assert.fail);
+      close(window).then(done).catch(assert.fail);
     });
 
     tabs.open(url);
-  }).then(null, assert.fail);
+  }).catch(assert.fail);
 };
 
 // TEST: onClose event handler
 exports.testTabsEvent_onClose = function*(assert) {
   let window = yield open().then(focus);
   let url = "data:text/html;charset=utf-8,onclose";
   let eventCount = 0;
 
@@ -616,17 +616,17 @@ exports.testTabsEvent_onCloseWindow = fu
       onClose: endTest
     });
 
     tabs.open({
       url: "data:text/html;charset=utf-8,tab4",
       onOpen: testCasePossiblyLoaded,
       onClose: endTest
     });
-  }).then(null, assert.fail);
+  }).catch(assert.fail);
 }
 
 // TEST: onReady event handler
 exports.testTabsEvent_onReady = function(assert, done) {
   open().then(focus).then(window => {
     let url = "data:text/html;charset=utf-8,onready";
     let eventCount = 0;
 
@@ -640,17 +640,17 @@ exports.testTabsEvent_onReady = function
     tabs.on('ready', function listener2(tab) {
       assert.equal(++eventCount, 2, "both listeners notified");
       tabs.removeListener('ready', listener1);
       tabs.removeListener('ready', listener2);
       close(window).then(done);
     });
 
     tabs.open(url);
-  }).then(null, assert.fail);
+  }).catch(assert.fail);
 };
 
 // TEST: onActivate event handler
 exports.testTabsEvent_onActivate = function(assert, done) {
   open().then(focus).then(window => {
     let url = "data:text/html;charset=utf-8,onactivate";
     let eventCount = 0;
 
@@ -660,21 +660,21 @@ exports.testTabsEvent_onActivate = funct
     };
     tabs.on('activate', listener1);
 
     // add listener via collection add
     tabs.on('activate', function listener2(tab) {
       assert.equal(++eventCount, 2, "both listeners notified");
       tabs.removeListener('activate', listener1);
       tabs.removeListener('activate', listener2);
-      close(window).then(done).then(null, assert.fail);
+      close(window).then(done).catch(assert.fail);
     });
 
     tabs.open(url);
-  }).then(null, assert.fail);
+  }).catch(assert.fail);
 };
 
 // onDeactivate event handler
 exports.testTabsEvent_onDeactivate = function*(assert) {
   let window = yield open().then(focus);
 
   let url = "data:text/html;charset=utf-8,ondeactivate";
   let eventCount = 0;
@@ -721,21 +721,21 @@ exports.testTabsEvent_pinning = function
       tabs.removeListener('pinned', onPinned);
       assert.ok(tab.isPinned, "notified tab is pinned");
       tab.unpin();
     });
 
     tabs.on('unpinned', function onUnpinned(tab) {
       tabs.removeListener('unpinned', onUnpinned);
       assert.ok(!tab.isPinned, "notified tab is not pinned");
-      close(window).then(done).then(null, assert.fail);
+      close(window).then(done).catch(assert.fail);
     });
 
     tabs.open(url);
-  }).then(null, assert.fail);
+  }).catch(assert.fail);
 };
 
 // TEST: per-tab event handlers
 exports.testPerTabEvents = function*(assert) {
   let window = yield open().then(focus);
   let eventCount = 0;
 
   let tab = yield new Promise(resolve => {
@@ -835,19 +835,19 @@ exports.testAttachOnMultipleDocuments = 
     });
 
     function checkEnd() {
       if (detachEventCount != 2)
         return;
 
       assert.pass("Got all detach events");
 
-      close(window).then(done).then(null, assert.fail);
+      close(window).then(done).catch(assert.fail);
     }
-  }).then(null, assert.fail);
+  }).catch(assert.fail);
 }
 
 
 exports.testAttachWrappers = function (assert, done) {
   // Check that content script has access to wrapped values by default
   open().then(focus).then(window => {
     let document = "data:text/html;charset=utf-8,<script>var globalJSVar = true; " +
                    "                       document.getElementById = 3;</script>";
@@ -861,22 +861,22 @@ exports.testAttachWrappers = function (a
                          '  self.postMessage(!("globalJSVar" in window));' +
                          '  self.postMessage(typeof window.globalJSVar == "undefined");' +
                          '} catch(e) {' +
                          '  self.postMessage(e.message);' +
                          '}',
           onMessage: function (msg) {
             assert.equal(msg, true, "Worker has wrapped objects ("+count+")");
             if (count++ == 1)
-              close(window).then(done).then(null, assert.fail);
+              close(window).then(done).catch(assert.fail);
           }
         });
       }
     });
-  }).then(null, assert.fail);
+  }).catch(assert.fail);
 }
 
 /*
 // We do not offer unwrapped access to DOM since bug 601295 landed
 // See 660780 to track progress of unwrap feature
 exports.testAttachUnwrapped = function (assert, done) {
   // Check that content script has access to unwrapped values through unsafeWindow
   openBrowserWindow(function(window, browser) {
@@ -926,34 +926,34 @@ exports['test window focus changes activ
 
           function whenReady(tab) {
             assert.pass("activate was called on windows focus change.");
             assert.equal(tab.url, url1, 'the activated tab url is correct');
 
             return close(win2).then(function() {
               assert.pass('window 2 was closed');
               return close(win1);
-            }).then(done).then(null, assert.fail);
+            }).then(done).catch(assert.fail);
           }
         });
 
         win1.focus();
       });
     }, "data:text/html;charset=utf-8,test window focus changes active tab</br><h1>Window #2");
   }, url1);
 };
 
 exports['test ready event on new window tab'] = function(assert, done) {
   let uri = encodeURI("data:text/html;charset=utf-8,Waiting for ready event!");
 
   require("sdk/tabs").on("ready", function onReady(tab) {
     if (tab.url === uri) {
       require("sdk/tabs").removeListener("ready", onReady);
       assert.pass("ready event was emitted");
-      close(window).then(done).then(null, assert.fail);
+      close(window).then(done).catch(assert.fail);
     }
   });
 
   let window = openBrowserWindow(function(){}, uri);
 };
 
 exports['test unique tab ids'] = function(assert, done) {
   var windows = require('sdk/windows').browserWindows;

--- a/addon-sdk/source/test/test-addon-window.js
+++ b/addon-sdk/source/test/test-addon-window.js
@@ -11,12 +11,12 @@ exports.testReady = function(assert, don
   let windowIsReady = false;
 
   ready.then(function() {
     assert.equal(windowIsReady, false, 'ready promise was resolved only once');
     windowIsReady = true;
 
     loader.unload();
     done();
-  }).then(null, assert.fail);
+  }).catch(assert.fail);
 }
 
 require('sdk/test').run(exports);

--- a/addon-sdk/source/test/test-child_process.js
+++ b/addon-sdk/source/test/test-child_process.js
@@ -61,17 +61,17 @@ exports.testExecOptionsEnvironment = fun
       env: { CHILD_PROCESS_ENV_TEST: 'my-value-test' }
     }, function (err, stdout, stderr) {
       assert.equal(stderr, '', 'stderr is empty');
       assert.ok(!err, 'received `cwd` option');
       assert.ok(/my-value-test/.test(stdout),
         'receives environment option');
       done();
     });
-  }).then(null, assert.fail);
+  }).catch(assert.fail);
 };
 
 exports.testExecOptionsTimeout = function (assert, done) {
   let count = 0;
   getScript('wait').then(script => {
     let child = exec(script, { timeout: 100 }, (err, stdout, stderr) => {
       assert.equal(err.killed, true, 'error has `killed` property as true');
       assert.equal(err.code, null, 'error has `code` as null');
@@ -99,29 +99,29 @@ exports.testExecOptionsTimeout = functio
     child.on('exit', exitHandler);
     child.on('close', closeHandler);
 
     function complete () {
       child.off('exit', exitHandler);
       child.off('close', closeHandler);
       done();
     }
-  }).then(null, assert.fail);
+  }).catch(assert.fail);
 };
 
 exports.testExecFileCallbackSuccess = function (assert, done) {
   getScript('args').then(script => {
     execFile(script, ['--myargs', '-j', '-s'], { cwd: PROFILE_DIR }, function (err, stdout, stderr) {
       assert.ok(!err, 'no errors found');
       assert.equal(stderr, '', 'stderr is empty');
       // Trim output since different systems have different new line output
       assert.equal(stdout.trim(), '--myargs -j -s'.trim(), 'passes in correct arguments');
       done();
     });
-  }).then(null, assert.fail);
+  }).catch(assert.fail);
 };
 
 exports.testExecFileCallbackError = function (assert, done) {
   execFile('not-real-command', { cwd: PROFILE_DIR }, function (err, stdout, stderr) {
     assert.ok(/Executable not found/.test(err.message),
       `error '${err.message}' contains error message`);
     assert.ok(err.lineNumber >= 0, 'error contains lineNumber');
     assert.ok(/resource:\/\//.test(err.fileName), 'error contains fileName');
@@ -138,17 +138,17 @@ exports.testExecFileOptionsEnvironment =
       env: { CHILD_PROCESS_ENV_TEST: 'my-value-test' }
     }, function (err, stdout, stderr) {
       assert.equal(stderr, '', 'stderr is empty');
       assert.ok(!err, 'received `cwd` option');
       assert.ok(/my-value-test/.test(stdout),
         'receives environment option');
       done();
     });
-  }).then(null, assert.fail);
+  }).catch(assert.fail);
 };
 
 exports.testExecFileOptionsTimeout = function (assert, done) {
   let count = 0;
   getScript('wait').then(script => {
     let child = execFile(script, { timeout: 100 }, (err, stdout, stderr) => {
       assert.equal(err.killed, true, 'error has `killed` property as true');
       assert.equal(err.code, null, 'error has `code` as null');
@@ -176,17 +176,17 @@ exports.testExecFileOptionsTimeout = fun
     child.on('exit', exitHandler);
     child.on('close', closeHandler);
 
     function complete () {
       child.off('exit', exitHandler);
       child.off('close', closeHandler);
       done();
     }
-  }).then(null, assert.fail);
+  }).catch(assert.fail);
 };
 
 /**
  * Not necessary to test for both `exec` and `execFile`, but
  * it is necessary to test both when the buffer is larger
  * and smaller than buffer size used by the subprocess library (1024)
  */
 exports.testExecFileOptionsMaxBufferLargeStdOut = function (assert, done) {
@@ -199,17 +199,17 @@ exports.testExecFileOptionsMaxBufferLarg
       assert.ok(/stdout maxBuffer exceeded/.test(err.toString()),
         'error contains stdout maxBuffer exceeded message');
       assert.ok(stdout.length >= 50, 'stdout has full buffer');
       assert.equal(stderr, '', 'stderr is empty');
       if (++count === 3) complete();
     });
     stdoutChild.on('exit', exitHandler);
     stdoutChild.on('close', closeHandler);
-  }).then(null, assert.fail);
+  }).catch(assert.fail);
 
   function exitHandler (code, signal) {
     assert.equal(code, null, 'Exit code is null in exit handler');
     assert.equal(signal, 'SIGTERM', 'Signal is SIGTERM in exit handler');
     if (++count === 3) complete();
   }
 
   function closeHandler (code, signal) {
@@ -234,17 +234,17 @@ exports.testExecFileOptionsMaxBufferLarg
       assert.ok(/stderr maxBuffer exceeded/.test(err.toString()),
         'error contains stderr maxBuffer exceeded message');
       assert.ok(stderr.length >= 50, 'stderr has full buffer');
       assert.equal(stdout, '', 'stdout is empty');
       if (++count === 3) complete();
     });
     stderrChild.on('exit', exitHandler);
     stderrChild.on('close', closeHandler);
-  }).then(null, assert.fail);
+  }).catch(assert.fail);
 
   function exitHandler (code, signal) {
     assert.equal(code, null, 'Exit code is null in exit handler');
     assert.equal(signal, 'SIGTERM', 'Signal is SIGTERM in exit handler');
     if (++count === 3) complete();
   }
 
   function closeHandler (code, signal) {
@@ -275,17 +275,17 @@ exports.testExecFileOptionsMaxBufferSmal
       assert.ok(/stdout maxBuffer exceeded/.test(err.toString()),
         'error contains stdout maxBuffer exceeded message');
       assert.ok(stdout.length >= 50, 'stdout has full buffer');
       assert.equal(stderr, '', 'stderr is empty');
       if (++count === 3) complete();
     });
     stdoutChild.on('exit', exitHandler);
     stdoutChild.on('close', closeHandler);
-  }).then(null, assert.fail);
+  }).catch(assert.fail);
 
   function exitHandler (code, signal) {
     // Sometimes the buffer limit is hit before the process closes successfully
     // on both OSX/Windows
     if (code === null) {
       assert.equal(code, null, 'Exit code is null in exit handler');
       assert.equal(signal, 'SIGTERM', 'Signal is SIGTERM in exit handler');
     }
@@ -326,17 +326,17 @@ exports.testExecFileOptionsMaxBufferSmal
       assert.ok(/stderr maxBuffer exceeded/.test(err.toString()),
         'error contains stderr maxBuffer exceeded message');
       assert.ok(stderr.length >= 50, 'stderr has full buffer');
       assert.equal(stdout, '', 'stdout is empty');
       if (++count === 3) complete();
     });
     stderrChild.on('exit', exitHandler);
     stderrChild.on('close', closeHandler);
-  }).then(null, assert.fail);
+  }).catch(assert.fail);
 
   function exitHandler (code, signal) {
     // Sometimes the buffer limit is hit before the process closes successfully
     // on both OSX/Windows
     if (code === null) {
       assert.equal(code, null, 'Exit code is null in exit handler');
       assert.equal(signal, 'SIGTERM', 'Signal is SIGTERM in exit handler');
     }
@@ -372,17 +372,17 @@ exports.testChildExecFileKillSignal = fu
   getScript('wait').then(script => {
     execFile(script, {
       killSignal: 'beepbeep',
       timeout: 10
     }, function (err, stdout, stderr) {
       assert.equal(err.signal, 'beepbeep', 'correctly used custom killSignal');
       done();
     });
-  }).then(null, assert.fail);
+  }).catch(assert.fail);
 };
 
 exports.testChildProperties = function (assert, done) {
   getScript('check-env').then(script => {
     let child = spawn(script, {
       env: { CHILD_PROCESS_ENV_TEST: 'my-value-test' }
     });
 
@@ -503,17 +503,17 @@ exports.testSpawnOptions = function (ass
     cwdChild = spawn(checkPwd, { cwd: PROFILE_DIR });
 
     // Do these need to be unbound?
     envChild.stdout.on('data', data => envStdout += data);
     cwdChild.stdout.on('data', data => cwdStdout += data);
 
     envChild.on('close', envClose);
     cwdChild.on('close', cwdClose);
-  }).then(null, assert.fail);
+  }).catch(assert.fail);
 
   function envClose () {
     assert.equal(envStdout.trim(), 'my-value-test', 'spawn correctly passed in ENV');
     if (++count === 2) complete();
   }
 
   function cwdClose () {
     // Check for PROFILE_DIR in the output because

--- a/addon-sdk/source/test/test-native-loader.js
+++ b/addon-sdk/source/test/test-native-loader.js
@@ -232,17 +232,17 @@ for (let variant of variants) {
         manifest: manifest,
         isNative: true
       });
 
       let program = main(loader);
       testLoader(program, assert);
       unload(loader);
       done();
-    }).then(null, (reason) => console.error(reason));
+    }).catch((reason) => console.error(reason));
   };
 
   exports[`test require#resolve with relative, dependencies (${variant.description})`] = function(assert, done) {
     getJSON('/fixtures/native-addon-test/package.json').then(manifest => {
       let rootURI = variant.getRootURI('native-addon-test');
       let loader = Loader({
         paths: makePaths(rootURI),
         rootURI: rootURI,
@@ -260,17 +260,17 @@ for (let variant of variants) {
       assert.equal(program.require.resolve("modules/Promise.jsm"), "resource://gre/modules/Promise.jsm", "works with path lookups");
 
       // TODO bug 1050422, handle loading non JS/JSM file paths
       // assert.equal(program.require.resolve("test-assets/styles.css"), fixtureRoot + "node_modules/test-assets/styles.css",
       // "works with different file extension lookups in dependencies");
 
       unload(loader);
       done();
-    }).then(null, (reason) => console.error(reason));
+    }).catch((reason) => console.error(reason));
   };
 }
 
 before(exports, () => {
   for (let fixture of fixtures) {
     let url = `jar:${root}/fixtures/${fixture}.xpi!/`;
 
     resProto.setSubstitution(fixture, NetUtil.newURI(url));
@@ -304,17 +304,17 @@ exports['test JSM loading'] = function (
       program.isLoadedAbsolute(20),
       program.isLoadedJSAbsolute(30)
     ]).then(([path, absolute, jsabsolute]) => {
       assert.equal(path, 10, 'JSM files resolved from path work');
       assert.equal(absolute, 20, 'JSM files resolved from full resource:// work');
       assert.equal(jsabsolute, 30, 'JS files resolved from full resource:// work');
     }).then(done, console.error);
 
-  }).then(null, console.error);
+  }).catch(console.error);
 };
 
 function testLoader (program, assert) {
   // Test 'main' entries
   // no relative custom main `lib/index.js`
   assert.equal(program.customMainModule, 'custom entry file',
     'a node_module dependency correctly uses its `main` entry in manifest');
   // relative custom main `./lib/index.js`
@@ -383,12 +383,12 @@ function loadAddon (uri, map) {
       rootURI: rootURI,
       manifest: manifest,
       isNative: true,
       modules: {
         '@test/options': testOptions
       }
     });
     let program = main(loader);
-  }).then(null, console.error);
+  }).catch(console.error);
 }
 
 require('sdk/test').run(exports);

--- a/addon-sdk/source/test/test-panel.js
+++ b/addon-sdk/source/test/test-panel.js
@@ -1016,17 +1016,17 @@ exports['test panel CSS'] = function(ass
       assert.equal(div.offsetHeight, 120,
         "Panel contentStyleFile worked");
 
       assert.equal(window.getComputedStyle(div).borderTopStyle, "dashed",
         "Panel contentStyleFile with relative path worked");
 
         loader.unload();
         done();
-      }).then(null, assert.fail);
+      }).catch(assert.fail);
     }
   });
 
   panel.show();
 };
 
 exports['test panel contentScriptFile'] = function(assert, done) {
   const { merge } = require("sdk/util/object");

--- a/addon-sdk/source/test/test-promise.js
+++ b/addon-sdk/source/test/test-promise.js
@@ -112,22 +112,22 @@ exports['test error recovery with promis
     let deferred = defer();
     deferred.resolve('recovery');
     return deferred.promise;
   }).then(function(actual) {
     assert.equal(actual, 'recovery', 'recorvered via promise');
     let deferred = defer();
     deferred.reject('error');
     return deferred.promise;
-  }).then(null, function(actual) {
+  }).catch(function(actual) {
     assert.equal(actual, 'error', 'rejected via promise');
     let deferred = defer();
     deferred.reject('end');
     return deferred.promise;
-  }).then(null, function(actual) {
+  }).catch(function(actual) {
     assert.equal(actual, 'end', 'rejeced via promise');
     done();
   });
 
   deferred.reject('reason');
 };
 
 exports['test propagation'] = function(assert, done) {
@@ -145,27 +145,27 @@ exports['test propagation'] = function(a
 
 exports['test chaining'] = function(assert, done) {
   let boom = Error('boom'), brax = Error('braxXXx');
   let deferred = defer();
 
   deferred.promise.then().then().then(function(actual) {
     assert.equal(actual, 2, 'value propagates unchanged');
     return actual + 2;
-  }).then(null, function(reason) {
+  }).catch(function(reason) {
     assert.fail('should not reject');
   }).then(function(actual) {
     assert.equal(actual, 4, 'value propagates through if not handled');
     throw boom;
   }).then(function(actual) {
     assert.fail('exception must reject promise');
-  }).then().then(null, function(actual) {
+  }).then().catch(function(actual) {
     assert.equal(actual, boom, 'reason propagates unchanged');
     throw brax;
-  }).then().then(null, function(actual) {
+  }).then().catch(function(actual) {
     assert.equal(actual, brax, 'reason changed becase of exception');
     return 'recovery';
   }).then(function(actual) {
     assert.equal(actual, 'recovery', 'recovered from error');
     done();
   });
 
   deferred.resolve(2);
@@ -236,17 +236,17 @@ exports['test promised error handling'] 
 exports['test errors in promise resolution handlers are propagated'] = function(assert, done) {
   var expected = Error('Boom');
   var { promise, resolve } = defer();
 
   promise.then(function() {
     throw expected;
   }).then(function() {
     return undefined;
-  }).then(null, function(actual) {
+  }).catch(function(actual) {
     assert.equal(actual, expected, 'rejected as expected');
   }).then(done, assert.fail);
 
   resolve({});
 };
 
 exports['test return promise form promised'] = function(assert, done) {
   let f = promised(function() {
@@ -440,17 +440,17 @@ function testEnvironment ({all, resolve,
   all([resolve(5), resolve(10), 925]).then(val => {
     assert.equal(val[0], 5, 'promise#all works ' + type);
     assert.equal(val[1], 10, 'promise#all works ' + type);
     assert.equal(val[2], 925, 'promise#all works ' + type);
     return resolve(1000);
   }).then(value => {
     assert.equal(value, 1000, 'promise#resolve works ' + type);
     return reject('testing reject');
-  }).then(null, reason => {
+  }).catch(reason => {
     assert.equal(reason, 'testing reject', 'promise#reject works ' + type);
     let deferred = defer();
     setTimeout(() => deferred.resolve('\\m/'), 10);
     return deferred.promise;
   }).then(value => {
     assert.equal(value, '\\m/', 'promise#defer works ' + type);
     return promised(x => x * x)(5);
   }).then(value => {

--- a/addon-sdk/source/test/test-ui-toggle-button.js
+++ b/addon-sdk/source/test/test-ui-toggle-button.js
@@ -1200,17 +1200,17 @@ exports['test button checked'] = functio
           'clicked:foo', 'changed:foo:false', 'clicked:foo', 'changed:foo:true'
         ],
         'button change events works');
 
       close(window).
         then(loader.unload).
         then(done, assert.fail);
     })
-  }).then(null, assert.fail);
+  }).catch(assert.fail);
 }
 
 exports['test button is checked on window level'] = function(assert, done) {
   let loader = Loader(module);
   let { ToggleButton } = loader.require('sdk/ui');
   let { browserWindows } = loader.require('sdk/windows');
   let tabs = loader.require('sdk/tabs');
 
@@ -1262,17 +1262,17 @@ exports['test button is checked on windo
           'window state, checked is `false`.');
 
         tab.close(()=> {
           close(window).
             then(loader.unload).
             then(done, assert.fail);
         })
       }).
-      then(null, assert.fail);
+      catch(assert.fail);
     }
   });
 
 };
 
 exports['test button click do not messing up states'] = function(assert) {
   let loader = Loader(module);
   let { ToggleButton } = loader.require('sdk/ui');

--- a/addon-sdk/source/test/test-window-utils-private-browsing.js
+++ b/addon-sdk/source/test/test-window-utils-private-browsing.js
@@ -74,17 +74,17 @@ exports.testWindowTrackerIgnoresPrivateW
 
     return close(window).then(function() {
       return makeEmptyBrowserWindow().then(function(window) {
         myNonPrivateWindow = window;
         assert.pass('opened new window');
         return close(window);
       });
     });
-  }).then(null, assert.fail);
+  }).catch(assert.fail);
 };
 
 // Test setting activeWIndow and onFocus for private windows
 exports.testSettingActiveWindowDoesNotIgnorePrivateWindow = function(assert, done) {
   let browserWindow = WM.getMostRecentWindow("navigator:browser");
 
   assert.equal(windowUtils.activeBrowserWindow, browserWindow,
                "Browser window is the active browser window.");
@@ -137,17 +137,17 @@ exports.testSettingActiveWindowDoesNotIg
     }).then(_ => {
       assert.strictEqual(windowUtils.activeBrowserWindow, browserWindow,
                          "Correct active browser window when pb mode is supported [4]");
       assert.strictEqual(windowUtils.activeWindow, browserWindow,
                          "Correct active window when pb mode is supported [4]");
 
       return close(window);
     })
-  }).then(done).then(null, assert.fail);
+  }).then(done).catch(assert.fail);
 };
 
 exports.testActiveWindowDoesNotIgnorePrivateWindow = function(assert, done) {
   // make a new private window
   makeEmptyBrowserWindow({
     private: true
   }).then(function(window) {
     // PWPB case
@@ -177,17 +177,17 @@ exports.testActiveWindowDoesNotIgnorePri
                    "active window is not private");
       assert.equal(isPrivate(windowUtils.activeBrowserWindow), false,
                    "active browser window is not private");
       assert.equal(isWindowPrivate(window), false, "window is not private");
       assert.equal(isPrivate(window), false, "window is not private");
     }
 
     return close(window);
-  }).then(done).then(null, assert.fail);
+  }).then(done).catch(assert.fail);
 }
 
 exports.testWindowIteratorIgnoresPrivateWindows = function(assert, done) {
   // make a new private window
   makeEmptyBrowserWindow({
     private: true
   }).then(function(window) {
     // PWPB case
@@ -199,12 +199,12 @@ exports.testWindowIteratorIgnoresPrivate
     // Global case
     else {
       assert.equal(isWindowPrivate(window), false, "window is not private");
       assert.ok(toArray(windowUtils.windowIterator()).indexOf(window) > -1,
                 "window is in windowIterator()");
     }
 
     return close(window);
-  }).then(done).then(null, assert.fail);
+  }).then(done).catch(assert.fail);
 };
 
 require("sdk/test").run(exports);

--- a/browser/base/content/aboutaccounts/aboutaccounts.js
+++ b/browser/base/content/aboutaccounts/aboutaccounts.js
@@ -440,31 +440,31 @@ function migrateToDevEdition(urlParams) 
     let accountData = JSON.parse(text).accountData;
     updateDisplayedEmail(accountData);
     return fxAccounts.setSignedInUser(accountData);
   }).then(() => {
     return fxAccounts.promiseAccountsForceSigninURI().then(url => {
       show("remote");
       wrapper.init(url, urlParams);
     });
-  }).then(null, error => {
+  }).catch(error => {
     log("Failed to migrate FX Account: " + error);
     show("stage", "intro");
     // load the remote frame in the background
     fxAccounts.promiseAccountsSignUpURI().then(uri => {
       wrapper.init(uri, urlParams)
     }).catch(e => {
       console.log("Failed to load signup page", e);
       setErrorPage("configError");
     });
   }).then(() => {
     // Reset the pref after migration.
     Services.prefs.setBoolPref("identity.fxaccounts.migrateToDevEdition", false);
     return true;
-  }).then(null, err => {
+  }).catch(err => {
     Cu.reportError("Failed to reset the migrateToDevEdition pref: " + err);
     return false;
   });
 }
 
 // Helper function that returns the path of the default profile on disk. Will be
 // overridden in tests.
 function getDefaultProfilePath() {

--- a/browser/base/content/browser.js
+++ b/browser/base/content/browser.js
@@ -1669,17 +1669,17 @@ var gBrowserInit = {
       Cu.reportError("Could not end startup crash tracking: " + ex);
     }
 
     // Delay this a minute into the idle time because there's no rush.
     requestIdleCallback(() => {
       this.gmpInstallManager = new GMPInstallManager();
       // We don't really care about the results, if someone is interested they
       // can check the log.
-      this.gmpInstallManager.simpleCheckAndInstall().then(null, () => {});
+      this.gmpInstallManager.simpleCheckAndInstall().catch(() => {});
     }, {timeout: 1000 * 60});
 
     SessionStore.promiseInitialized.then(() => {
       // Bail out if the window has been closed in the meantime.
       if (window.closed) {
         return;
       }
 

--- a/browser/base/content/sanitizeDialog.js
+++ b/browser/base/content/sanitizeDialog.js
@@ -98,19 +98,19 @@ var gSanitizePromptDialog = {
     let docElt = document.documentElement;
     let acceptButton = docElt.getButton("accept");
     acceptButton.disabled = true;
     acceptButton.setAttribute("label",
                               this.bundleBrowser.getString("sanitizeButtonClearing"));
     docElt.getButton("cancel").disabled = true;
 
     try {
-      s.sanitize().then(null, Components.utils.reportError)
+      s.sanitize().catch(Components.utils.reportError)
                   .then(() => window.close())
-                  .then(null, Components.utils.reportError);
+                  .catch(Components.utils.reportError);
       return false;
     } catch (er) {
       Components.utils.reportError("Exception during sanitize: " + er);
       return true; // We *do* want to close immediately on error.
     }
   },
 
   /**

--- a/browser/components/customizableui/CustomizeMode.jsm
+++ b/browser/components/customizableui/CustomizeMode.jsm
@@ -421,17 +421,17 @@ CustomizeMode.prototype = {
           this.panelUIContents.setAttribute("showoutline", "true");
         }
         delete this._enableOutlinesTimeout;
       }, 0);
 
       if (!this._wantToBeInCustomizeMode) {
         this.exit();
       }
-    })().then(null, e => {
+    })().catch(e => {
       log.error("Error entering customize mode", e);
       // We should ensure this has been called, and calling it again doesn't hurt:
       window.PanelUI.endBatchUpdate();
       this._handler.isEnteringCustomizeMode = false;
       // Exit customize mode to ensure proper clean-up when entering failed.
       this.exit();
     });
   },
@@ -591,17 +591,17 @@ CustomizeMode.prototype = {
       this._transitioning = false;
       this._handler.isExitingCustomizeMode = false;
       CustomizableUI.dispatchToolboxEvent("aftercustomization", {}, window);
       CustomizableUI.notifyEndCustomizing(window);
 
       if (this._wantToBeInCustomizeMode) {
         this.enter();
       }
-    })().then(null, e => {
+    })().catch(e => {
       log.error("Error exiting customize mode", e);
       if (!gPhotonStructure) {
         // We should ensure this has been called, and calling it again doesn't hurt:
         window.PanelUI.endBatchUpdate();
       }
       this._handler.isExitingCustomizeMode = false;
     });
   },
@@ -861,17 +861,17 @@ CustomizeMode.prototype = {
         } else if (provider == CustomizableUI.PROVIDER_SPECIAL) {
           this.visiblePalette.removeChild(paletteChild);
         }
 
         paletteChild = nextChild;
       }
       this.visiblePalette.hidden = false;
       this.window.gNavToolbox.palette = this._stowedPalette;
-    })().then(null, log.error);
+    })().catch(log.error);
   },
 
   isCustomizableItem(aNode) {
     return aNode.localName == "toolbarbutton" ||
            aNode.localName == "toolbaritem" ||
            aNode.localName == "toolbarseparator" ||
            aNode.localName == "toolbarspring" ||
            aNode.localName == "toolbarspacer";
@@ -1067,17 +1067,17 @@ CustomizeMode.prototype = {
     let target = CustomizableUI.getCustomizeTargetForArea(aArea, this.window);
     if (!target || this.areas.has(target)) {
       return null;
     }
 
     this._addDragHandlers(target);
     for (let child of target.children) {
       if (this.isCustomizableItem(child) && !this.isWrappedToolbarItem(child)) {
-        await this.deferredWrapToolbarItem(child, CustomizableUI.getPlaceForItem(child)).then(null, log.error);
+        await this.deferredWrapToolbarItem(child, CustomizableUI.getPlaceForItem(child)).catch(log.error);
       }
     }
     this.areas.add(target);
     return target;
   },
 
   _wrapToolbarItemSync(aArea) {
     let target = CustomizableUI.getCustomizeTargetForArea(aArea, this.window);
@@ -1144,17 +1144,17 @@ CustomizeMode.prototype = {
         for (let toolbarItem of target.children) {
           if (this.isWrappedToolbarItem(toolbarItem)) {
             await this.deferredUnwrapToolbarItem(toolbarItem);
           }
         }
         this._removeDragHandlers(target);
       }
       this.areas.clear();
-    })().then(null, log.error);
+    })().catch(log.error);
   },
 
   _removeExtraToolbarsIfEmpty() {
     let toolbox = this.window.gNavToolbox;
     for (let child of toolbox.children) {
       if (child.hasAttribute("customindex")) {
         let placements = CustomizableUI.getWidgetIdsInArea(child.id);
         if (!placements.length) {
@@ -1200,17 +1200,17 @@ CustomizeMode.prototype = {
       this._updateResetButton();
       this._updateUndoResetButton();
       this._updateEmptyPaletteNotice();
       this._showPanelCustomizationPlaceholders();
       this.resetting = false;
       if (!this._wantToBeInCustomizeMode) {
         this.exit();
       }
-    })().then(null, log.error);
+    })().catch(log.error);
   },
 
   undoReset() {
     this.resetting = true;
 
     return (async () => {
       this._removePanelCustomizationPlaceholders();
       await this.depopulatePalette();
@@ -1224,17 +1224,17 @@ CustomizeMode.prototype = {
       this.populatePalette();
 
       this.persistCurrentSets(true);
 
       this._updateResetButton();
       this._updateUndoResetButton();
       this._updateEmptyPaletteNotice();
       this.resetting = false;
-    })().then(null, log.error);
+    })().catch(log.error);
   },
 
   _onToolbarVisibilityChange(aEvent) {
     let toolbar = aEvent.target;
     if (aEvent.detail.visible && toolbar.getAttribute("customizable") == "true") {
       toolbar.setAttribute("customizing", "true");
     } else {
       toolbar.removeAttribute("customizing");

--- a/browser/components/customizableui/content/panelUI.js
+++ b/browser/components/customizableui/content/panelUI.js
@@ -439,17 +439,17 @@ const PanelUI = {
           CustomizableUI.registerMenuPanel(this.contents, CustomizableUI.AREA_PANEL);
         } finally {
           this.endBatchUpdate();
         }
       }
       this._updateQuitTooltip();
       this.panel.hidden = false;
       this._isReady = true;
-    })().then(null, Cu.reportError);
+    })().catch(Cu.reportError);
 
     return this._readyPromise;
   },
 
   /**
    * Switch the panel to the main view if it's not already
    * in that view.
    */

--- a/browser/components/downloads/DownloadsCommon.jsm
+++ b/browser/components/downloads/DownloadsCommon.jsm
@@ -462,17 +462,17 @@ this.DownloadsCommon = {
         aFile.launch();
       } catch (ex) {
         // If launch fails, try sending it through the system's external "file:"
         // URL handler.
         Cc["@mozilla.org/uriloader/external-protocol-service;1"]
           .getService(Ci.nsIExternalProtocolService)
           .loadUrl(NetUtil.newURI(aFile));
       }
-    }).then(null, Cu.reportError);
+    }).catch(Cu.reportError);
   },
 
   /**
    * Show a downloaded file in the system file manager.
    *
    * @param aFile
    *        a downloaded file.
    */
@@ -669,17 +669,17 @@ function DownloadsDataCtor(aPrivate) {
 DownloadsDataCtor.prototype = {
   /**
    * Starts receiving events for current downloads.
    */
   initializeDataLink() {
     if (!this._dataLinkInitialized) {
       let promiseList = Downloads.getList(this._isPrivate ? Downloads.PRIVATE
                                                           : Downloads.PUBLIC);
-      promiseList.then(list => list.addView(this)).then(null, Cu.reportError);
+      promiseList.then(list => list.addView(this)).catch(Cu.reportError);
       this._dataLinkInitialized = true;
     }
   },
   _dataLinkInitialized: false,
 
   /**
    * Iterator for all the available Download objects. This is empty until the
    * data has been loaded using the JavaScript API for downloads.
@@ -703,17 +703,17 @@ DownloadsDataCtor.prototype = {
 
   /**
    * Asks the back-end to remove finished downloads from the list.
    */
   removeFinished() {
     let promiseList = Downloads.getList(this._isPrivate ? Downloads.PRIVATE
                                                         : Downloads.PUBLIC);
     promiseList.then(list => list.removeFinished())
-               .then(null, Cu.reportError);
+               .catch(Cu.reportError);
     let indicatorData = this._isPrivate ? PrivateDownloadsIndicatorData
                                         : DownloadsIndicatorData;
     indicatorData.attention = DownloadsCommon.ATTENTION_NONE;
   },
 
   // Integration with the asynchronous Downloads back-end
 
   onDownloadAdded(download) {

--- a/browser/components/downloads/DownloadsTaskbar.jsm
+++ b/browser/components/downloads/DownloadsTaskbar.jsm
@@ -105,17 +105,17 @@ this.DownloadsTaskbar = {
       Downloads.getSummary(Downloads.ALL).then(summary => {
         // In case the method is re-entered, we simply ignore redundant
         // invocations of the callback, instead of keeping separate state.
         if (this._summary) {
           return undefined;
         }
         this._summary = summary;
         return this._summary.addView(this);
-      }).then(null, Cu.reportError);
+      }).catch(Cu.reportError);
     }
   },
 
   /**
    * On Windows, attaches the taskbar indicator to the specified browser window.
    */
   _attachIndicator(aWindow) {
     // Activate the indicator on the specified window.

--- a/browser/components/nsBrowserGlue.js
+++ b/browser/components/nsBrowserGlue.js
@@ -1208,17 +1208,17 @@ BrowserGlue.prototype = {
       }
       if (newProfile) {
         // We don't want a default profile with Developer Edition settings, an
         // empty profile directory will do. The profile service of the other
         // Firefox will populate it with its own stuff.
         let newProfilePath = newProfile.rootDir.path;
         OS.File.removeDir(newProfilePath).then(() => {
           return OS.File.makeDir(newProfilePath);
-        }).then(null, e => {
+        }).catch(e => {
           Cu.reportError("Could not empty profile 'default': " + e);
         });
       }
     }
   },
 
   _onQuitRequest: function BG__onQuitRequest(aCancelQuit, aQuitType) {
     // If user has already dismissed quit request, then do nothing

--- a/browser/components/places/content/browserPlacesViews.js
+++ b/browser/components/places/content/browserPlacesViews.js
@@ -1637,17 +1637,17 @@ PlacesToolbar.prototype = {
   },
 
   _onDrop: function PT__onDrop(aEvent) {
     PlacesControllerDragHelper.currentDropTarget = aEvent.target;
 
     let dropPoint = this._getDropPoint(aEvent);
     if (dropPoint && dropPoint.ip) {
       PlacesControllerDragHelper.onDrop(dropPoint.ip, aEvent.dataTransfer)
-                                .then(null, Components.utils.reportError);
+                                .catch(Components.utils.reportError);
       aEvent.preventDefault();
     }
 
     this._cleanupDragDetails();
     aEvent.stopPropagation();
   },
 
   _onDragExit: function PT__onDragExit(aEvent) {

--- a/browser/components/places/content/controller.js
+++ b/browser/components/places/content/controller.js
@@ -212,40 +212,40 @@ PlacesController.prototype = {
 
   doCommand: function PC_doCommand(aCommand) {
     switch (aCommand) {
     case "cmd_undo":
       if (!PlacesUIUtils.useAsyncTransactions) {
         PlacesUtils.transactionManager.undoTransaction();
         return;
       }
-      PlacesTransactions.undo().then(null, Components.utils.reportError);
+      PlacesTransactions.undo().catch(Components.utils.reportError);
       break;
     case "cmd_redo":
       if (!PlacesUIUtils.useAsyncTransactions) {
         PlacesUtils.transactionManager.redoTransaction();
         return;
       }
-      PlacesTransactions.redo().then(null, Components.utils.reportError);
+      PlacesTransactions.redo().catch(Components.utils.reportError);
       break;
     case "cmd_cut":
     case "placesCmd_cut":
       this.cut();
       break;
     case "cmd_copy":
     case "placesCmd_copy":
       this.copy();
       break;
     case "cmd_paste":
     case "placesCmd_paste":
-      this.paste().then(null, Components.utils.reportError);
+      this.paste().catch(Components.utils.reportError);
       break;
     case "cmd_delete":
     case "placesCmd_delete":
-      this.remove("Remove Selection").then(null, Components.utils.reportError);
+      this.remove("Remove Selection").catch(Components.utils.reportError);
       break;
     case "placesCmd_deleteDataHost":
       var host;
       if (PlacesUtils.nodeIsHost(this._view.selectedNode)) {
         var queries = this._view.selectedNode.getQueries();
         host = queries[0].domain;
       } else
         host = NetUtil.newURI(this._view.selectedNode.uri).host;
@@ -281,17 +281,17 @@ PlacesController.prototype = {
       break;
     case "placesCmd_moveBookmarks":
       this.moveSelectedBookmarks();
       break;
     case "placesCmd_reload":
       this.reloadSelectedLivemark();
       break;
     case "placesCmd_sortBy:name":
-      this.sortFolderByName().then(null, Components.utils.reportError);
+      this.sortFolderByName().catch(Components.utils.reportError);
       break;
     case "placesCmd_createBookmark":
       let node = this._view.selectedNode;
       PlacesUIUtils.showBookmarkDialog({ action: "add"
                                        , type: "bookmark"
                                        , hiddenRows: [ "description"
                                                      , "keyword"
                                                      , "location"

--- a/browser/components/places/content/menu.xml
+++ b/browser/components/places/content/menu.xml
@@ -358,17 +358,17 @@
       ]]></handler>
 
       <handler event="drop"><![CDATA[
         PlacesControllerDragHelper.currentDropTarget = event.target;
 
         let dropPoint = this._getDropPoint(event);
         if (dropPoint && dropPoint.ip) {
           PlacesControllerDragHelper.onDrop(dropPoint.ip, event.dataTransfer)
-                                    .then(null, Components.utils.reportError);
+                                    .catch(Components.utils.reportError);
           event.preventDefault();
         }
 
         this._cleanupDragDetails();
         event.stopPropagation();
       ]]></handler>
 
       <handler event="dragover"><![CDATA[

--- a/browser/components/places/content/moveBookmarks.js
+++ b/browser/components/places/content/moveBookmarks.js
@@ -49,17 +49,17 @@ var gMoveBookmarksDialog = {
       let newParentGuid = await PlacesUtils.promiseItemGuid(selectedFolderId);
       for (let node of this._nodes) {
         // Nothing to do if the node is already under the selected folder.
         if (node.parent.itemId == selectedFolderId)
           continue;
         await PlacesTransactions.Move({ guid: node.bookmarkGuid
                                       , newParentGuid }).transact();
       }
-    }).then(null, Components.utils.reportError);
+    }).catch(Components.utils.reportError);
   },
 
   newFolder: function MBD_newFolder() {
     // The command is disabled when the tree is not focused
     this.foldersTree.focus();
     goDoCommand("placesCmd_new:folder");
   }
 };

--- a/browser/components/places/content/places.js
+++ b/browser/components/places/content/places.js
@@ -369,17 +369,17 @@ var PlacesOrganizer = {
    * Open a file-picker and import the selected file into the bookmarks store
    */
   importFromFile: function PO_importFromFile() {
     let fp = Cc["@mozilla.org/filepicker;1"].createInstance(Ci.nsIFilePicker);
     let fpCallback = function fpCallback_done(aResult) {
       if (aResult != Ci.nsIFilePicker.returnCancel && fp.fileURL) {
         Components.utils.import("resource://gre/modules/BookmarkHTMLUtils.jsm");
         BookmarkHTMLUtils.importFromURL(fp.fileURL.spec, false)
-                         .then(null, Components.utils.reportError);
+                         .catch(Components.utils.reportError);
       }
     };
 
     fp.init(window, PlacesUIUtils.getString("SelectImport"),
             Ci.nsIFilePicker.modeOpen);
     fp.appendFilters(Ci.nsIFilePicker.filterHTML);
     fp.open(fpCallback);
   },
@@ -388,17 +388,17 @@ var PlacesOrganizer = {
    * Allows simple exporting of bookmarks.
    */
   exportBookmarks: function PO_exportBookmarks() {
     let fp = Cc["@mozilla.org/filepicker;1"].createInstance(Ci.nsIFilePicker);
     let fpCallback = function fpCallback_done(aResult) {
       if (aResult != Ci.nsIFilePicker.returnCancel) {
         Components.utils.import("resource://gre/modules/BookmarkHTMLUtils.jsm");
         BookmarkHTMLUtils.exportToFile(fp.file.path)
-                         .then(null, Components.utils.reportError);
+                         .catch(Components.utils.reportError);
       }
     };
 
     fp.init(window, PlacesUIUtils.getString("EnterExport"),
             Ci.nsIFilePicker.modeSave);
     fp.appendFilters(Ci.nsIFilePicker.filterHTML);
     fp.defaultString = "bookmarks.html";
     fp.open(fpCallback);

--- a/browser/components/places/content/treeView.js
+++ b/browser/components/places/content/treeView.js
@@ -1352,17 +1352,17 @@ PlacesTreeView.prototype = {
 
   drop: function PTV_drop(aRow, aOrientation, aDataTransfer) {
     // We are responsible for translating the |index| and |orientation|
     // parameters into a container id and index within the container,
     // since this information is specific to the tree view.
     let ip = this._getInsertionPoint(aRow, aOrientation);
     if (ip) {
       PlacesControllerDragHelper.onDrop(ip, aDataTransfer)
-                                .then(null, Components.utils.reportError);
+                                .catch(Components.utils.reportError);
     }
 
     PlacesControllerDragHelper.currentDropTarget = null;
   },
 
   getParentIndex: function PTV_getParentIndex(aRow) {
     let [, parentRow] = this._getParentByChildRow(aRow);
     return parentRow;

--- a/browser/components/privatebrowsing/test/browser/browser_privatebrowsing_downloadLastDir_c.js
+++ b/browser/components/privatebrowsing/test/browser/browser_privatebrowsing_downloadLastDir_c.js
@@ -73,17 +73,17 @@ function test() {
          "LastDir should be the expected last dir");
       // gDownloadLastDir should be usable outside of private windows
       is(gDownloadLastDir.file.path, aGlobalLastDir.path,
          "gDownloadLastDir should be the expected global last dir");
 
       gDownloadLastDir.cleanupPrivateFile();
       aWin.close();
       aCallback();
-    }).then(null, function() { ok(false); });
+    }).catch(function() { ok(false); });
   }
 
   testOnWindow(false, function(win, downloadDir) {
     testDownloadDir(win, downloadDir, file1, tmpDir, dir1, dir1, function() {
       testOnWindow(true, function(win1, downloadDir1) {
         testDownloadDir(win1, downloadDir1, file2, dir1, dir1, dir2, function() {
           testOnWindow(false, function(win2, downloadDir2) {
             testDownloadDir(win2, downloadDir2, file3, dir1, dir3, dir3, finish);

--- a/browser/components/uitour/UITour.jsm
+++ b/browser/components/uitour/UITour.jsm
@@ -645,17 +645,17 @@ this.UITour = {
             let onPopupShown = () => {
               searchbar.textbox.popup.removeEventListener("popupshown", onPopupShown);
               this.sendPageCallback(messageManager, data.callbackID);
             };
 
             searchbar.textbox.popup.addEventListener("popupshown", onPopupShown);
             searchbar.openSuggestionsPanel();
           }
-        }).then(null, Cu.reportError);
+        }).catch(Cu.reportError);
         break;
       }
 
       case "ping": {
         if (typeof data.callbackID == "string")
           this.sendPageCallback(messageManager, data.callbackID);
         break;
       }

--- a/browser/components/uitour/test/browser_UITour.js
+++ b/browser/components/uitour/test/browser_UITour.js
@@ -154,17 +154,17 @@ var tests = [
         gContentAPI.showHighlight("appMenu");
         waitForElementToBeVisible(highlight, function() {
           isnot(PanelUI.panel.state, "closed",
                 "Panel should remain open since UITour didn't open it in the first place");
           gContentAPI.hideMenu("appMenu");
           done();
         }, "Highlight should move to the appMenu button");
       }, "Highlight should be shown after showHighlight() for fixed panel items");
-    }).then(null, Components.utils.reportError);
+    }).catch(Components.utils.reportError);
   },
   function test_highlight_effect(done) {
     function waitForHighlightWithEffect(highlightEl, effect, next, error) {
       return waitForCondition(() => highlightEl.getAttribute("active") == effect,
                               next,
                               error);
     }
     function checkDefaultEffect() {

--- a/browser/components/uitour/test/browser_UITour2.js
+++ b/browser/components/uitour/test/browser_UITour2.js
@@ -58,17 +58,17 @@ var tests = [
                 ok(!PanelUI.panel.hasAttribute("noautohide"), "@noautohide on the menu panel should have been cleaned up on close");
                 done();
               });
               gContentAPI.hideMenu("appMenu");
             }, "Info should move to the appMenu button");
           });
         }, "Info should be shown after showInfo() for fixed menu panel items");
       });
-    }).then(null, Components.utils.reportError);
+    }).catch(Components.utils.reportError);
   },
   taskify(async function test_bookmarks_menu() {
     let bookmarksMenuButton = document.getElementById("bookmarks-menu-button");
 
     is(bookmarksMenuButton.open, false, "Menu should initially be closed");
     gContentAPI.showMenu("bookmarks");
 
     await waitForConditionPromise(() => {

--- a/browser/experiments/test/addons/experiment-racybranch/bootstrap.js
+++ b/browser/experiments/test/addons/experiment-racybranch/bootstrap.js
@@ -21,14 +21,14 @@ function realstartup() {
   let experiment = experiments._getActiveExperiment();
   if (experiment.branch) {
     Cu.reportError("Found pre-existing branch: " + experiment.branch);
     return;
   }
 
   let branch = "racy-set";
   experiments.setExperimentBranch(experiment.id, branch)
-    .then(null, Cu.reportError);
+    .catch(Cu.reportError);
 }
 
 function shutdown() { }
 function install() { }
 function uninstall() { }

--- a/browser/extensions/pdfjs/content/web/viewer.js
+++ b/browser/extensions/pdfjs/content/web/viewer.js
@@ -1294,17 +1294,17 @@ var PDFViewerApplication = {
     }
     if (!this.downloadComplete) {
       downloadByUrl();
       return;
     }
     this.pdfDocument.getData().then(function getDataSuccess(data) {
       var blob = (0, _pdfjsLib.createBlob)(data, 'application/pdf');
       downloadManager.download(blob, url, filename);
-    }, downloadByUrl).then(null, downloadByUrl);
+    }, downloadByUrl).catch(downloadByUrl);
   },
   fallback: function pdfViewFallback(featureId) {
     if (this.fellback) {
       return;
     }
     this.fellback = true;
     this.externalServices.fallback({
       featureId,

--- a/browser/extensions/pocket/content/main.js
+++ b/browser/extensions/pocket/content/main.js
@@ -559,17 +559,17 @@ var pktUI = (function() {
     function isInOverflowMenu() {
         var subview = getSubview();
         return !!subview;
     }
 
     function getFirefoxAccountSignedInUser(callback) {
         fxAccounts.getSignedInUser().then(userData => {
             callback(userData);
-        }).then(null, error => {
+        }).catch(error => {
             callback();
         });
     }
 
     function getUILocale() {
         return Services.locale.getAppLocaleAsLangTag();
     }
 

--- a/browser/extensions/screenshots/webextension/background/takeshot.js
+++ b/browser/extensions/screenshots/webextension/background/takeshot.js
@@ -42,18 +42,17 @@ this.takeshot = (function() {
       shot.abTests = shotAbTests;
     }
     return catcher.watchPromise(capturePromise.then(() => {
       return browser.tabs.create({url: shot.creatingUrl})
     }).then((tab) => {
       openedTab = tab;
       return uploadShot(shot);
     }).then(() => {
-      return browser.tabs.update(openedTab.id, {url: shot.viewUrl}).then(
-        null,
+      return browser.tabs.update(openedTab.id, {url: shot.viewUrl}).catch(
         (error) => {
           // FIXME: If https://bugzilla.mozilla.org/show_bug.cgi?id=1365718 is resolved,
           // use the errorCode added as an additional check:
           if ((/invalid tab id/i).test(error)) {
             // This happens if the tab was closed before the upload completed
             return browser.tabs.create({url: shot.viewUrl});
           }
           throw error;

--- a/browser/modules/AboutHome.jsm
+++ b/browser/modules/AboutHome.jsm
@@ -182,14 +182,14 @@ var AboutHome = {
       }
 
       if (target && target.messageManager) {
         target.messageManager.sendAsyncMessage("AboutHome:Update", data);
       } else {
         let mm = Cc["@mozilla.org/globalmessagemanager;1"].getService(Ci.nsIMessageListenerManager);
         mm.broadcastAsyncMessage("AboutHome:Update", data);
       }
-    }).then(null, function onError(x) {
+    }).catch(function onError(x) {
       Cu.reportError("Error in AboutHome.sendAboutHomeData: " + x);
     });
   },
 
 };

--- a/devtools/client/canvasdebugger/panel.js
+++ b/devtools/client/canvasdebugger/panel.js
@@ -45,17 +45,17 @@ CanvasDebuggerPanel.prototype = {
         this.panelWin.gFront = new CanvasFront(this.target.client, this.target.form);
         return this.panelWin.startupCanvasDebugger();
       })
       .then(() => {
         this.isReady = true;
         this.emit("ready");
         return this;
       })
-      .then(null, function onError(aReason) {
+      .catch(function onError(aReason) {
         DevToolsUtils.reportException("CanvasDebuggerPanel.prototype.open", aReason);
       });
   },
 
   // DevToolPanel API
 
   get target() {
     return this._toolbox.target;

--- a/devtools/client/canvasdebugger/test/head.js
+++ b/devtools/client/canvasdebugger/test/head.js
@@ -121,17 +121,17 @@ function ifTestingSupported() {
 
 function ifTestingUnsupported() {
   todo(false, "Skipping test because some required functionality isn't supported.");
   finish();
 }
 
 function test() {
   let generator = isTestingSupported() ? ifTestingSupported : ifTestingUnsupported;
-  Task.spawn(generator).then(null, handleError);
+  Task.spawn(generator).catch(handleError);
 }
 
 function createCanvas() {
   return document.createElementNS("http://www.w3.org/1999/xhtml", "canvas");
 }
 
 function isTestingSupported() {
   if (!gRequiresWebGL) {

--- a/devtools/client/commandline/test/helpers.js
+++ b/devtools/client/commandline/test/helpers.js
@@ -129,17 +129,17 @@ var { helpers, assert } = (function () {
     options.tab = tabbrowser.addTab();
     tabbrowser.selectedTab = options.tab;
     options.browser = tabbrowser.getBrowserForTab(options.tab);
     options.target = TargetFactory.forTab(options.tab);
 
     var loaded = helpers.listenOnce(options.browser, "load", true).then(function (ev) {
       var reply = callback.call(null, options);
 
-      return Promise.resolve(reply).then(null, function (error) {
+      return Promise.resolve(reply).catch(function (error) {
         ok(false, error);
       }).then(function () {
         tabbrowser.removeTab(options.tab);
 
         delete options.target;
         delete options.browser;
         delete options.tab;
 
@@ -325,17 +325,17 @@ var { helpers, assert } = (function () {
 
       return win.DeveloperToolbar.show(true).then(function () {
         var toolbar = win.DeveloperToolbar;
         innerOptions.automator = createDeveloperToolbarAutomator(toolbar);
         innerOptions.requisition = toolbar.requisition;
 
         var reply = callback.call(null, innerOptions);
 
-        return Promise.resolve(reply).then(null, function (error) {
+        return Promise.resolve(reply).catch(function (error) {
           ok(false, error);
           console.error(error);
         }).then(function () {
           win.DeveloperToolbar.hide().then(function () {
             delete innerOptions.automator;
           });
         });
       });

--- a/devtools/client/debugger/panel.js
+++ b/devtools/client/debugger/panel.js
@@ -64,17 +64,17 @@ DebuggerPanel.prototype = {
 
           let keyShortcut = this.translateToKeyShortcut(keycode, modifiers);
           this._toolbox.useKeyWithSplitConsole(keyShortcut, handler, "jsdebugger");
         }
         this.isReady = true;
         this.emit("ready");
         return this;
       })
-      .then(null, function onError(aReason) {
+      .catch(function onError(aReason) {
         DevToolsUtils.reportException("DebuggerPanel.prototype.open", aReason);
       });
   },
 
   /**
    * Translate a VK_ keycode, with modifiers, to a key shortcut that can be used with
    * shared/key-shortcut.
    *

--- a/devtools/client/debugger/test/mochitest/browser_dbg_addonactor.js
+++ b/devtools/client/debugger/test/mochitest/browser_dbg_addonactor.js
@@ -26,17 +26,17 @@ function test() {
     installAddon()
       .then(attachAddonActorForId.bind(null, gClient, ADDON3_ID))
       .then(attachAddonThread)
       .then(testDebugger)
       .then(testSources)
       .then(() => gClient.close())
       .then(uninstallAddon)
       .then(finish)
-      .then(null, aError => {
+      .catch(aError => {
         ok(false, "Got an error: " + aError.message + "\n" + aError.stack);
       });
   });
 }
 
 function installAddon() {
   return addTemporaryAddon(ADDON3_PATH).then(aAddon => {
     gAddon = aAddon;

--- a/devtools/client/debugger/test/mochitest/browser_dbg_auto-pretty-print-02.js
+++ b/devtools/client/debugger/test/mochitest/browser_dbg_auto-pretty-print-02.js
@@ -55,17 +55,17 @@ function test() {
       yield selectFirstSource();
       testFirstSourceLabel();
       testPrettyPrintButtonOn();
 
       // Disable auto pretty printing so it does not affect the following tests.
       yield disableAutoPrettyPrint();
 
       closeDebuggerAndFinish(gPanel)
-        .then(null, aError => {
+        .catch(aError => {
           ok(false, "Got an error: " + DevToolsUtils.safeErrorString(aError));
         });
     });
 
     function selectSecondSource() {
       let finished = waitForDebuggerEvents(gPanel, gDebugger.EVENTS.SOURCE_SHOWN, 2);
       gSources.selectedIndex = 1;
       return finished;

--- a/devtools/client/debugger/test/mochitest/browser_dbg_blackboxing-01.js
+++ b/devtools/client/debugger/test/mochitest/browser_dbg_blackboxing-01.js
@@ -19,17 +19,17 @@ function test() {
   initDebugger(TAB_URL, options).then(([aTab,, aPanel]) => {
     gTab = aTab;
     gPanel = aPanel;
     gDebugger = gPanel.panelWin;
 
     testBlackBoxSource()
       .then(testBlackBoxReload)
       .then(() => closeDebuggerAndFinish(gPanel))
-      .then(null, aError => {
+      .catch(aError => {
         ok(false, "Got an error: " + aError.message + "\n" + aError.stack);
       });
   });
 }
 
 function testBlackBoxSource() {
   const bbButton = getBlackBoxButton(gPanel);
   ok(!bbButton.checked, "Should not be black boxed by default");

--- a/devtools/client/debugger/test/mochitest/browser_dbg_blackboxing-02.js
+++ b/devtools/client/debugger/test/mochitest/browser_dbg_blackboxing-02.js
@@ -23,17 +23,17 @@ function test() {
     gTab = aTab;
     gPanel = aPanel;
     gDebugger = gPanel.panelWin;
     gFrames = gDebugger.DebuggerView.StackFrames;
 
     testBlackBoxSource()
       .then(testBlackBoxStack)
       .then(() => resumeDebuggerThenCloseAndFinish(gPanel))
-      .then(null, aError => {
+      .catch(aError => {
         ok(false, "Got an error: " + aError.message + "\n" + aError.stack);
       });
   });
 }
 
 function testBlackBoxSource() {
   return toggleBlackBoxing(gPanel).then(source => {
     ok(source.isBlackBoxed, "The source should be black boxed now.");

--- a/devtools/client/debugger/test/mochitest/browser_dbg_blackboxing-03.js
+++ b/devtools/client/debugger/test/mochitest/browser_dbg_blackboxing-03.js
@@ -25,17 +25,17 @@ function test() {
     gDebugger = gPanel.panelWin;
     gFrames = gDebugger.DebuggerView.StackFrames;
     gSources = gDebugger.DebuggerView.Sources;
 
     waitForSourceAndCaretAndScopes(gPanel, ".html", 21)
       .then(testBlackBoxStack)
       .then(testBlackBoxSource)
       .then(() => resumeDebuggerThenCloseAndFinish(gPanel))
-      .then(null, aError => {
+      .catch(aError => {
         ok(false, "Got an error: " + aError.message + "\n" + aError.stack);
       });
 
     callInTab(gTab, "runTest");
   });
 }
 
 function testBlackBoxStack() {

--- a/devtools/client/debugger/test/mochitest/browser_dbg_blackboxing-04.js
+++ b/devtools/client/debugger/test/mochitest/browser_dbg_blackboxing-04.js
@@ -24,17 +24,17 @@ function test() {
     gPanel = aPanel;
     gDebugger = gPanel.panelWin;
     gFrames = gDebugger.DebuggerView.StackFrames;
     gSources = gDebugger.DebuggerView.Sources;
 
     blackBoxSources()
       .then(testBlackBoxStack)
       .then(() => resumeDebuggerThenCloseAndFinish(gPanel))
-      .then(null, aError => {
+      .catch(aError => {
         ok(false, "Got an error: " + aError.message + "\n" + aError.stack);
       });
   });
 }
 
 function blackBoxSources() {
   let finished = waitForThreadEvents(gPanel, "blackboxchange", 3);
 

--- a/devtools/client/debugger/test/mochitest/browser_dbg_blackboxing-05.js
+++ b/devtools/client/debugger/test/mochitest/browser_dbg_blackboxing-05.js
@@ -25,17 +25,17 @@ function test() {
     gDeck = gDebugger.document.getElementById("editor-deck");
 
     testSourceEditorShown();
     toggleBlackBoxing(gPanel)
       .then(testBlackBoxMessageShown)
       .then(clickStopBlackBoxingButton)
       .then(testSourceEditorShownAgain)
       .then(() => closeDebuggerAndFinish(gPanel))
-      .then(null, aError => {
+      .catch(aError => {
         ok(false, "Got an error: " + aError.message + "\n" + aError.stack);
       });
   });
 }
 
 function testSourceEditorShown() {
   is(gDeck.selectedIndex, "0",
     "The first item in the deck should be selected (the source editor).");

--- a/devtools/client/debugger/test/mochitest/browser_dbg_blackboxing-06.js
+++ b/devtools/client/debugger/test/mochitest/browser_dbg_blackboxing-06.js
@@ -22,17 +22,17 @@ function test() {
     gTab = aTab;
     gPanel = aPanel;
     gDebugger = gPanel.panelWin;
     gSources = gDebugger.DebuggerView.Sources;
 
     waitForCaretAndScopes(gPanel, 21)
       .then(testBlackBox)
       .then(() => resumeDebuggerThenCloseAndFinish(gPanel))
-      .then(null, aError => {
+      .catch(aError => {
         ok(false, "Got an error: " + aError.message + "\n" + aError.stack);
       });
 
     callInTab(gTab, "runTest");
   });
 }
 
 function testBlackBox() {

--- a/devtools/client/debugger/test/mochitest/browser_dbg_blackboxing-07.js
+++ b/devtools/client/debugger/test/mochitest/browser_dbg_blackboxing-07.js
@@ -19,17 +19,17 @@ function test() {
   initDebugger(TAB_URL, options).then(([aTab,, aPanel]) => {
     gTab = aTab;
     gPanel = aPanel;
     gDebugger = gPanel.panelWin;
 
     testBlackBoxSource()
       .then(testBlackBoxReload)
       .then(() => closeDebuggerAndFinish(gPanel))
-      .then(null, aError => {
+      .catch(aError => {
         ok(false, "Got an error: " + aError.message + "\n" + aError.stack);
       });
   });
 }
 
 function testBlackBoxSource() {
   const bbButton = getBlackBoxButton(gPanel);
   ok(bbButton.checked, "Should be black boxed by default");

--- a/devtools/client/debugger/test/mochitest/browser_dbg_breadcrumbs-access.js
+++ b/devtools/client/debugger/test/mochitest/browser_dbg_breadcrumbs-access.js
@@ -24,17 +24,17 @@ function test() {
     gSources = gDebugger.DebuggerView.Sources;
     gFrames = gDebugger.DebuggerView.StackFrames;
 
     waitForSourceAndCaretAndScopes(gPanel, "-02.js", 6)
       .then(checkNavigationWhileNotFocused)
       .then(focusCurrentStackFrame)
       .then(checkNavigationWhileFocused)
       .then(() => resumeDebuggerThenCloseAndFinish(gPanel))
-      .then(null, aError => {
+      .catch(aError => {
         ok(false, "Got an error: " + aError.message + "\n" + aError.stack);
       });
 
     callInTab(gTab, "firstCall");
   });
 
   function checkNavigationWhileNotFocused() {
     checkState({ frame: 1, source: 1, line: 6 });

--- a/devtools/client/debugger/test/mochitest/browser_dbg_break-on-dom-event-01.js
+++ b/devtools/client/debugger/test/mochitest/browser_dbg_break-on-dom-event-01.js
@@ -28,17 +28,17 @@ function test() {
       .then(setupGlobals)
       .then(pauseDebuggee)
       .then(testBreakOnAll)
       .then(testBreakOnDisabled)
       .then(testBreakOnNone)
       .then(testBreakOnClick)
       .then(() => gClient.close())
       .then(finish)
-      .then(null, aError => {
+      .catch(aError => {
         ok(false, "Got an error: " + aError.message + "\n" + aError.stack);
       });
   });
 }
 
 function setupGlobals(aThreadClient) {
   gThreadClient = aThreadClient;
   gInput = content.document.querySelector("input");

--- a/devtools/client/debugger/test/mochitest/browser_dbg_break-on-dom-event-02.js
+++ b/devtools/client/debugger/test/mochitest/browser_dbg_break-on-dom-event-02.js
@@ -26,17 +26,17 @@ function test() {
 
     addTab(TAB_URL)
       .then(() => attachThreadActorForUrl(gClient, TAB_URL))
       .then(aThreadClient => gThreadClient = aThreadClient)
       .then(pauseDebuggee)
       .then(testBreakOnClick)
       .then(() => gClient.close())
       .then(finish)
-      .then(null, aError => {
+      .catch(aError => {
         ok(false, "Got an error: " + aError.message + "\n" + aError.stack);
       });
   });
 }
 
 function pauseDebuggee() {
   let deferred = promise.defer();
 

--- a/devtools/client/debugger/test/mochitest/browser_dbg_chrome-debugging.js
+++ b/devtools/client/debugger/test/mochitest/browser_dbg_chrome-debugging.js
@@ -30,17 +30,17 @@ function test() {
   gClient = new DebuggerClient(transport);
   gClient.connect().then(([aType, aTraits]) => {
     is(aType, "browser",
       "Root actor should identify itself as a browser.");
 
     promise.all([gAttached.promise, gNewGlobal.promise, gNewChromeSource.promise])
       .then(resumeAndCloseConnection)
       .then(finish)
-      .then(null, aError => {
+      .catch(aError => {
         ok(false, "Got an error: " + aError.message + "\n" + aError.stack);
       });
 
     testChromeActor();
   });
 }
 
 function testChromeActor() {

--- a/devtools/client/debugger/test/mochitest/browser_dbg_clean-exit-window.js
+++ b/devtools/client/debugger/test/mochitest/browser_dbg_clean-exit-window.js
@@ -17,17 +17,17 @@ function test() {
     .then(([aTab, aDebuggee, aPanel, aWindow]) => {
       gDebuggee = aDebuggee;
       gPanel = aPanel;
       gDebugger = gPanel.panelWin;
       gWindow = aWindow;
 
       return testCleanExit();
     })
-    .then(null, aError => {
+    .catch(aError => {
       ok(false, "Got an error: " + aError.message + "\n" + aError.stack);
     });
 }
 
 function testCleanExit() {
   let deferred = promise.defer();
 
   ok(!!gWindow, "Second window created.");

--- a/devtools/client/debugger/test/mochitest/browser_dbg_closure-inspection.js
+++ b/devtools/client/debugger/test/mochitest/browser_dbg_closure-inspection.js
@@ -16,17 +16,17 @@ function test() {
   };
   initDebugger(TAB_URL, options).then(([aTab,, aPanel]) => {
     gTab = aTab;
     gPanel = aPanel;
     gDebugger = gPanel.panelWin;
 
     testClosure()
       .then(() => resumeDebuggerThenCloseAndFinish(gPanel))
-      .then(null, aError => {
+      .catch(aError => {
         ok(false, "Got an error: " + aError.message + "\n" + aError.stack);
       });
   });
 
   function testClosure() {
     generateMouseClickInTab(gTab, "content.document.querySelector('button')");
 
     return waitForDebuggerEvents(gPanel, gDebugger.EVENTS.FETCHED_SCOPES).then(() => {

--- a/devtools/client/debugger/test/mochitest/browser_dbg_debugger-statement.js
+++ b/devtools/client/debugger/test/mochitest/browser_dbg_debugger-statement.js
@@ -28,17 +28,17 @@ function test() {
       .then((aTab) => {
         gTab = aTab;
         return attachTabActorForUrl(gClient, TAB_URL);
       })
       .then(testEarlyDebuggerStatement)
       .then(testDebuggerStatement)
       .then(() => gClient.close())
       .then(finish)
-      .then(null, aError => {
+      .catch(aError => {
         ok(false, "Got an error: " + aError.message + "\n" + aError.stack);
       });
   });
 }
 
 function testEarlyDebuggerStatement([aGrip, aResponse]) {
   let deferred = promise.defer();
 

--- a/devtools/client/debugger/test/mochitest/browser_dbg_editor-contextmenu.js
+++ b/devtools/client/debugger/test/mochitest/browser_dbg_editor-contextmenu.js
@@ -20,17 +20,17 @@ function test() {
   initDebugger(TAB_URL, options).then(([aTab,, aPanel]) => {
     gTab = aTab;
     gPanel = aPanel;
     gDebugger = gPanel.panelWin;
     gEditor = gDebugger.DebuggerView.editor;
     gSources = gDebugger.DebuggerView.Sources;
     gContextMenu = gDebugger.document.getElementById("sourceEditorContextMenu");
 
-    waitForSourceAndCaretAndScopes(gPanel, "-02.js", 1).then(performTest).then(null, info);
+    waitForSourceAndCaretAndScopes(gPanel, "-02.js", 1).then(performTest).catch(info);
     callInTab(gTab, "firstCall");
   });
 
   function performTest() {
     is(gDebugger.gThreadClient.state, "paused",
       "Should only be getting stack frames while paused.");
     is(gSources.itemCount, 2,
       "Found the expected number of sources.");
@@ -45,17 +45,17 @@ function test() {
     ok(gContextMenu,
       "The source editor's context menupopup is available.");
     ok(gEditor.getOption("readOnly"),
       "The source editor is read only.");
 
     gEditor.focus();
     gEditor.setSelection({ line: 1, ch: 0 }, { line: 1, ch: 10 });
 
-    once(gContextMenu, "popupshown").then(testContextMenu).then(null, info);
+    once(gContextMenu, "popupshown").then(testContextMenu).catch(info);
     gContextMenu.openPopup(gEditor.container, "overlap", 0, 0, true, false);
   }
 
   function testContextMenu() {
     let document = gDebugger.document;
 
     ok(document.getElementById("editMenuCommands"),
       "#editMenuCommands found.");

--- a/devtools/client/debugger/test/mochitest/browser_dbg_editor-mode.js
+++ b/devtools/client/debugger/test/mochitest/browser_dbg_editor-mode.js
@@ -25,17 +25,17 @@ function test() {
     gEditor = gDebugger.DebuggerView.editor;
     gSources = gDebugger.DebuggerView.Sources;
 
     waitForSourceAndCaretAndScopes(gPanel, "code_test-editor-mode", 1)
       .then(testInitialSource)
       .then(testSwitch1)
       .then(testSwitch2)
       .then(() => resumeDebuggerThenCloseAndFinish(gPanel))
-      .then(null, aError => {
+      .catch(aError => {
         ok(false, "Got an error: " + aError.message + "\n" + aError.stack);
       });
 
     callInTab(gTab, "firstCall");
   });
 }
 
 function testInitialSource() {

--- a/devtools/client/debugger/test/mochitest/browser_dbg_event-listeners-01.js
+++ b/devtools/client/debugger/test/mochitest/browser_dbg_event-listeners-01.js
@@ -28,17 +28,17 @@ function test() {
       .then((aTab) => {
         gTab = aTab;
         return attachThreadActorForUrl(gClient, TAB_URL);
       })
       .then(pauseDebuggee)
       .then(testEventListeners)
       .then(() => gClient.close())
       .then(finish)
-      .then(null, aError => {
+      .catch(aError => {
         ok(false, "Got an error: " + aError.message + "\n" + aError.stack);
       });
   });
 }
 
 function pauseDebuggee(aThreadClient) {
   let deferred = promise.defer();
 

--- a/devtools/client/debugger/test/mochitest/browser_dbg_event-listeners-02.js
+++ b/devtools/client/debugger/test/mochitest/browser_dbg_event-listeners-02.js
@@ -29,17 +29,17 @@ function test() {
       .then((aTab) => {
         gTab = aTab;
         return attachThreadActorForUrl(gClient, TAB_URL);
       })
       .then(pauseDebuggee)
       .then(testEventListeners)
       .then(() => gClient.close())
       .then(finish)
-      .then(null, aError => {
+      .catch(aError => {
         ok(false, "Got an error: " + aError.message + "\n" + aError.stack);
       });
   });
 }
 
 function pauseDebuggee(aThreadClient) {
   let deferred = promise.defer();
 

--- a/devtools/client/debugger/test/mochitest/browser_dbg_event-listeners-03.js
+++ b/devtools/client/debugger/test/mochitest/browser_dbg_event-listeners-03.js
@@ -29,17 +29,17 @@ function test() {
       .then((aTab) => {
         gTab = aTab;
         return attachThreadActorForUrl(gClient, TAB_URL);
       })
       .then(pauseDebuggee)
       .then(testEventListeners)
       .then(() => gClient.close())
       .then(finish)
-      .then(null, aError => {
+      .catch(aError => {
         ok(false, "Got an error: " + aError.message + "\n" + aError.stack);
       });
   });
 }
 
 function pauseDebuggee(aThreadClient) {
   let deferred = promise.defer();
 

--- a/devtools/client/debugger/test/mochitest/browser_dbg_iframes.js
+++ b/devtools/client/debugger/test/mochitest/browser_dbg_iframes.js
@@ -25,17 +25,17 @@ function test() {
     gIframe = gDebuggee.frames[0];
     gEditor = gDebugger.DebuggerView.editor;
     gSources = gDebugger.DebuggerView.Sources;
     gFrames = gDebugger.DebuggerView.StackFrames;
 
     checkIframeSource();
     checkIframePause()
       .then(() => resumeDebuggerThenCloseAndFinish(gPanel))
-      .then(null, aError => {
+      .catch(aError => {
         ok(false, "Got an error: " + aError.message + "\n" + aError.stack);
       });
   });
 
   function checkIframeSource() {
     is(gDebugger.gThreadClient.paused, false,
       "Should be running after starting the test.");
 

--- a/devtools/client/debugger/test/mochitest/browser_dbg_interrupts.js
+++ b/devtools/client/debugger/test/mochitest/browser_dbg_interrupts.js
@@ -29,17 +29,17 @@ function test() {
     gResumeKey = gDebugger.document.getElementById("resumeKey");
 
     gTarget.on("thread-paused", failOnPause);
     addBreakpoints()
       .then(() => { gTarget.off("thread-paused", failOnPause); })
       .then(testResumeButton)
       .then(testResumeKeyboard)
       .then(() => closeDebuggerAndFinish(gPanel))
-      .then(null, aError => {
+      .catch(aError => {
         ok(false, "Got an error: " + aError.message + "\n" + aError.stack);
       });
   });
 
   function failOnPause() {
     ok(false, "A pause was sent, but it shouldn't have been");
   }
 

--- a/devtools/client/debugger/test/mochitest/browser_dbg_jump-to-function-definition.js
+++ b/devtools/client/debugger/test/mochitest/browser_dbg_jump-to-function-definition.js
@@ -21,17 +21,17 @@ function test() {
   initDebugger(TAB_URL, options).then(([aTab,, aPanel]) => {
     gTab = aTab;
     gPanel = aPanel;
     gDebugger = gPanel.panelWin;
     gSources = gDebugger.DebuggerView.Sources;
 
     jumpToFunctionDefinition()
       .then(() => closeDebuggerAndFinish(gPanel))
-      .then(null, aError => {
+      .catch(aError => {
         ok(false, "Got an error: " + aError.message + "\n" + aError.stack);
       });
   });
 
   function jumpToFunctionDefinition() {
     let callLocation = {line: 5, ch: 0};
     let editor = gDebugger.DebuggerView.editor;
     let coords = editor.getCoordsFromPosition(callLocation);

--- a/devtools/client/debugger/test/mochitest/browser_dbg_listaddons.js
+++ b/devtools/client/debugger/test/mochitest/browser_dbg_listaddons.js
@@ -27,17 +27,17 @@ function test() {
 
     promise.resolve(null)
       .then(testFirstAddon)
       .then(testSecondAddon)
       .then(testRemoveFirstAddon)
       .then(testRemoveSecondAddon)
       .then(() => gClient.close())
       .then(finish)
-      .then(null, aError => {
+      .catch(aError => {
         ok(false, "Got an error: " + aError.message + "\n" + aError.stack);
       });
   });
 }
 
 function testFirstAddon() {
   let addonListChanged = false;
   gClient.addOneTimeListener("addonListChanged", () => {

--- a/devtools/client/debugger/test/mochitest/browser_dbg_listtabs-01.js
+++ b/devtools/client/debugger/test/mochitest/browser_dbg_listtabs-01.js
@@ -26,17 +26,17 @@ function test() {
 
     promise.resolve(null)
       .then(testFirstTab)
       .then(testSecondTab)
       .then(testRemoveTab)
       .then(testAttachRemovedTab)
       .then(() => gClient.close())
       .then(finish)
-      .then(null, aError => {
+      .catch(aError => {
         ok(false, "Got an error: " + aError.message + "\n" + aError.stack);
       });
   });
 }
 
 function testFirstTab() {
   return addTab(TAB1_URL).then(aTab => {
     gTab1 = aTab;

--- a/devtools/client/debugger/test/mochitest/browser_dbg_multiple-windows.js
+++ b/devtools/client/debugger/test/mochitest/browser_dbg_multiple-windows.js
@@ -30,17 +30,17 @@ function test() {
       .then(() => addTab(TAB1_URL))
       .then(testFirstTab)
       .then(() => addWindow(TAB2_URL))
       .then(testNewWindow)
       .then(testFocusFirst)
       .then(testRemoveTab)
       .then(() => gClient.close())
       .then(finish)
-      .then(null, aError => {
+      .catch(aError => {
         ok(false, "Got an error: " + aError.message + "\n" + aError.stack);
       });
   });
 }
 
 function testFirstTab(aTab) {
   let deferred = promise.defer();
 

--- a/devtools/client/debugger/test/mochitest/browser_dbg_navigation.js
+++ b/devtools/client/debugger/test/mochitest/browser_dbg_navigation.js
@@ -24,17 +24,17 @@ function test() {
     is(aType, "browser",
       "Root actor should identify itself as a browser.");
 
     addTab(TAB1_URL)
       .then(() => attachTabActorForUrl(gClient, TAB1_URL))
       .then(testNavigate)
       .then(testDetach)
       .then(finish)
-      .then(null, aError => {
+      .catch(aError => {
         ok(false, "Got an error: " + aError.message + "\n" + aError.stack);
       });
   });
 }
 
 function testNavigate([aGrip, aResponse]) {
   let outstanding = [promise.defer(), promise.defer()];