--- a/devtools/client/scratchpad/test/browser_scratchpad_contexts.js
+++ b/devtools/client/scratchpad/test/browser_scratchpad_contexts.js
@@ -1,67 +1,66 @@
 /* vim: set ts=2 et sw=2 tw=80: */
 /* Any copyright is dedicated to the Public Domain.
    http://creativecommons.org/publicdomain/zero/1.0/ */
+"use strict";
 
-function test()
-{
+function test() {
   waitForExplicitFinish();
 
   gBrowser.selectedTab = gBrowser.addTab();
   gBrowser.selectedBrowser.addEventListener("load", function onLoad() {
     gBrowser.selectedBrowser.removeEventListener("load", onLoad, true);
     openScratchpad(runTests);
   }, true);
 
   content.location = "data:text/html,test context switch in Scratchpad";
 }
 
-
-function runTests()
-{
+function runTests() {
   let sp = gScratchpadWindow.Scratchpad;
   let contentMenu = gScratchpadWindow.document.getElementById("sp-menu-content");
   let chromeMenu = gScratchpadWindow.document.getElementById("sp-menu-browser");
   let notificationBox = sp.notificationBox;
 
   ok(contentMenu, "found #sp-menu-content");
   ok(chromeMenu, "found #sp-menu-browser");
   ok(notificationBox, "found Scratchpad.notificationBox");
 
   let tests = [{
     method: "run",
-    prepare: function() {
+    prepare: function*() {
       sp.setContentContext();
 
       is(sp.executionContext, gScratchpadWindow.SCRATCHPAD_CONTEXT_CONTENT,
          "executionContext is content");
 
       is(contentMenu.getAttribute("checked"), "true",
          "content menuitem is checked");
 
       isnot(chromeMenu.getAttribute("checked"), "true",
          "chrome menuitem is not checked");
 
       ok(!notificationBox.currentNotification,
          "there is no notification in content context");
 
       sp.editor.setText("window.foobarBug636725 = 'aloha';");
 
-      ok(!content.wrappedJSObject.foobarBug636725,
-         "no content.foobarBug636725");
+      let pageResult = yield inContent(function*() {
+        return content.wrappedJSObject.foobarBug636725;
+      });
+      ok(!pageResult, "no content.foobarBug636725");
     },
-    then: function() {
+    then: function*() {
       is(content.wrappedJSObject.foobarBug636725, "aloha",
          "content.foobarBug636725 has been set");
     }
-  },
-  {
+  }, {
     method: "run",
-    prepare: function() {
+    prepare: function*() {
       sp.setBrowserContext();
 
       is(sp.executionContext, gScratchpadWindow.SCRATCHPAD_CONTEXT_BROWSER,
          "executionContext is chrome");
 
       is(chromeMenu.getAttribute("checked"), "true",
          "chrome menuitem is checked");
 
@@ -72,80 +71,75 @@ function runTests()
          "there is a notification in browser context");
 
       let [ from, to ] = sp.editor.getPosition(31, 32);
       sp.editor.replaceText("2'", from, to);
 
       is(sp.getText(), "window.foobarBug636725 = 'aloha2';",
          "setText() worked");
     },
-    then: function() {
+    then: function*() {
       is(window.foobarBug636725, "aloha2",
          "window.foobarBug636725 has been set");
 
       delete window.foobarBug636725;
       ok(!window.foobarBug636725, "no window.foobarBug636725");
     }
-  },
-  {
+  }, {
     method: "run",
-    prepare: function() {
+    prepare: function*() {
       sp.editor.replaceText("gBrowser", sp.editor.getPosition(7));
 
       is(sp.getText(), "window.gBrowser",
          "setText() worked with no end for the replace range");
     },
-    then: function([, , result]) {
+    then: function*([, , result]) {
       is(result.class, "XULElement",
          "chrome context has access to chrome objects");
     }
-  },
-  {
+  }, {
     method: "run",
-    prepare: function() {
+    prepare: function*() {
       // Check that the sandbox is cached.
       sp.editor.setText("typeof foobarBug636725cache;");
     },
-    then: function([, , result]) {
+    then: function*([, , result]) {
       is(result, "undefined", "global variable does not exist");
     }
-  },
-  {
+  }, {
     method: "run",
-    prepare: function() {
+    prepare: function*() {
       sp.editor.setText("window.foobarBug636725cache = 'foo';" +
                  "typeof foobarBug636725cache;");
     },
-    then: function([, , result]) {
+    then: function*([, , result]) {
       is(result, "string",
          "global variable exists across two different executions");
     }
-  },
-  {
+  }, {
     method: "run",
-    prepare: function() {
+    prepare: function*() {
       sp.editor.setText("window.foobarBug636725cache2 = 'foo';" +
                  "typeof foobarBug636725cache2;");
     },
-    then: function([, , result]) {
+    then: function*([, , result]) {
       is(result, "string",
          "global variable exists across two different executions");
     }
-  },
-  {
+  }, {
     method: "run",
-    prepare: function() {
+    prepare: function*() {
       sp.setContentContext();
 
       is(sp.executionContext, gScratchpadWindow.SCRATCHPAD_CONTEXT_CONTENT,
          "executionContext is content");
 
       sp.editor.setText("typeof foobarBug636725cache2;");
     },
-    then: function([, , result]) {
+    then: function*([, , result]) {
       is(result, "undefined",
          "global variable no longer exists after changing the context");
     }
   }];
 
   runAsyncCallbackTests(sp, tests).then(() => {
     sp.setBrowserContext();
     sp.editor.setText("delete foobarBug636725cache;" +

--- a/devtools/client/scratchpad/test/browser_scratchpad_execute_print.js
+++ b/devtools/client/scratchpad/test/browser_scratchpad_execute_print.js
@@ -1,89 +1,95 @@
 /* vim: set ts=2 et sw=2 tw=80: */
 /* Any copyright is dedicated to the Public Domain.
    http://creativecommons.org/publicdomain/zero/1.0/ */
+"use strict";
 
-function test()
-{
+function test() {
   waitForExplicitFinish();
 
   gBrowser.selectedTab = gBrowser.addTab();
   gBrowser.selectedBrowser.addEventListener("load", function onTabLoad() {
     gBrowser.selectedBrowser.removeEventListener("load", onTabLoad, true);
     openScratchpad(runTests);
   }, true);
 
   content.location = "data:text/html,<p>test run() and display() in Scratchpad";
 }
 
-
-function runTests()
-{
+function runTests() {
   let sp = gScratchpadWindow.Scratchpad;
   let tests = [{
     method: "run",
-    prepare: function() {
-      content.wrappedJSObject.foobarBug636725 = 1;
+    prepare: function*() {
+      yield inContent(function*() {
+        content.wrappedJSObject.foobarBug636725 = 1;
+      });
       sp.editor.setText("++window.foobarBug636725");
     },
-    then: function([code, , result]) {
+    then: function*([code, , result]) {
       is(code, sp.getText(), "code is correct");
-      is(result, content.wrappedJSObject.foobarBug636725,
+
+      let pageResult = yield inContent(function*() {
+        return content.wrappedJSObject.foobarBug636725;
+      });
+      is(result, pageResult,
          "result is correct");
 
       is(sp.getText(), "++window.foobarBug636725",
          "run() does not change the editor content");
 
-      is(content.wrappedJSObject.foobarBug636725, 2,
-         "run() updated window.foobarBug636725");
+      is(pageResult, 2, "run() updated window.foobarBug636725");
     }
-  },
-  {
+  }, {
     method: "display",
-    prepare: function() {},
-    then: function() {
-      is(content.wrappedJSObject.foobarBug636725, 3,
-         "display() updated window.foobarBug636725");
+    prepare: function*() {},
+    then: function*() {
+      let pageResult = yield inContent(function*() {
+        return content.wrappedJSObject.foobarBug636725;
+      });
+      is(pageResult, 3, "display() updated window.foobarBug636725");
 
       is(sp.getText(), "++window.foobarBug636725\n/*\n3\n*/",
          "display() shows evaluation result in the textbox");
 
       is(sp.editor.getSelection(), "\n/*\n3\n*/", "getSelection is correct");
     }
-  },
-  {
+  }, {
     method: "run",
-    prepare: function() {
+    prepare: function*() {
       sp.editor.setText("window.foobarBug636725 = 'a';\n" +
         "window.foobarBug636725 = 'b';");
       sp.editor.setSelection({ line: 0, ch: 0 }, { line: 0, ch: 29 });
     },
-    then: function([code, , result]) {
+    then: function*([code, , result]) {
       is(code, "window.foobarBug636725 = 'a';", "code is correct");
       is(result, "a", "result is correct");
 
       is(sp.getText(), "window.foobarBug636725 = 'a';\n" +
                        "window.foobarBug636725 = 'b';",
          "run() does not change the textbox value");
 
-      is(content.wrappedJSObject.foobarBug636725, "a",
-         "run() worked for the selected range");
+      let pageResult = yield inContent(function*() {
+        return content.wrappedJSObject.foobarBug636725;
+      });
+      is(pageResult, "a", "run() worked for the selected range");
     }
-  },
-  {
+  }, {
     method: "display",
-    prepare: function() {
+    prepare: function*() {
       sp.editor.setText("window.foobarBug636725 = 'c';\n" +
                  "window.foobarBug636725 = 'b';");
       sp.editor.setSelection({ line: 0, ch: 0 }, { line: 0, ch: 22 });
     },
-    then: function() {
-      is(content.wrappedJSObject.foobarBug636725, "a",
-         "display() worked for the selected range");
+    then: function*() {
+      let pageResult = yield inContent(function*() {
+        return content.wrappedJSObject.foobarBug636725;
+      });
+      is(pageResult, "a", "display() worked for the selected range");
 
       is(sp.getText(), "window.foobarBug636725" +
                        "\n/*\na\n*/" +
                        " = 'c';\n" +
                        "window.foobarBug636725 = 'b';",
          "display() shows evaluation result in the textbox");
 
       is(sp.editor.getSelection(), "\n/*\na\n*/", "getSelection is correct");

--- a/devtools/client/scratchpad/test/head.js
+++ b/devtools/client/scratchpad/test/head.js
@@ -186,31 +186,29 @@ function runAsyncTests(aScratchpad, aTes
  *          Scratchpad method to use, one of "run", "display", or "inspect".
  *        - prepare
  *          The callback to run just prior to executing the scratchpad method.
  *        - then
  *          The callback to run when the scratchpad execution promise resolves.
  * @return Promise
  *         The promise that will be resolved when all tests are finished.
  */
-function runAsyncCallbackTests(aScratchpad, aTests)
-{
-  let deferred = promise.defer();
+var runAsyncCallbackTests = Task.async(function*(aScratchpad, aTests) {
+  for (let {prepare, method, then} of aTests) {
+    yield prepare();
+    let res = yield aScratchpad[method]();
+    yield then(res);
+  }
+});
 
-  (function runTest() {
-    if (aTests.length) {
-      let test = aTests.shift();
-      test.prepare();
-      aScratchpad[test.method]().then(test.then.bind(test)).then(runTest);
-    } else {
-      deferred.resolve();
-    }
-  })();
-
-  return deferred.promise;
+/**
+ * A simple wrapper for ContentTask.spawn for more compact code.
+ */
+function inContent(generator, browser = gBrowser.selectedBrowser, args = {}) {
+  return ContentTask.spawn(browser, args, generator);
 }
 
 function cleanup()
 {
   if (gScratchpadWindow) {
     gScratchpadWindow.close();
     gScratchpadWindow = null;
   }