--- a/toolkit/.eslintrc.js
+++ b/toolkit/.eslintrc.js
@@ -149,17 +149,21 @@ module.exports = {
 
     // Error on newline where a semicolon is needed
     "no-unexpected-multiline": "error",
 
     // No unreachable statements
     "no-unreachable": "error",
 
     // No declaring variables that are never used
-    // "no-unused-vars": ["error", {"vars": "all", "args": "none"}],
+    // "no-unused-vars": ["error", {
+    //   "vars": "local",
+    //   "varsIgnorePattern": "^Cc|Ci|Cu|Cr|EXPORTED_SYMBOLS",
+    //   "args": "none",
+    // }],
 
     // No using variables before defined
     // "no-use-before-define": ["error", "nofunc"],
 
     // No using with
     "no-with": "error",
 
     // Always require semicolon at end of statement

new file mode 100644
--- /dev/null
+++ b/toolkit/components/.eslintrc.js
@@ -0,0 +1,11 @@
+"use strict";
+
+module.exports = {
+  "rules": {
+    "no-unused-vars": ["error", {
+      "vars": "local",
+      "varsIgnorePattern": "^Cc|Ci|Cu|Cr|EXPORTED_SYMBOLS",
+      "args": "none",
+    }]
+  }
+};

--- a/toolkit/components/aboutmemory/content/aboutMemory.js
+++ b/toolkit/components/aboutmemory/content/aboutMemory.js
@@ -1222,17 +1222,17 @@ function fillInTree(aRoot)
       let kid = aT._kids[0];
       let kidBytes = fillInNonLeafNodes(kid);
       aT._unsafeName += '/' + kid._unsafeName;
       if (kid._kids) {
         aT._kids = kid._kids;
       } else {
         delete aT._kids;
       }
-      aT._amount = kid._amount;
+      aT._amount = kidBytes;
       aT._description = kid._description;
       if (kid._nMerged !== undefined) {
         aT._nMerged = kid._nMerged
       }
       assert(!aT._hideKids && !kid._hideKids, "_hideKids set when merging");
 
     } else {
       // Non-leaf node with multiple children.  Derive its _amount and

--- a/toolkit/components/aboutperformance/content/aboutPerformance.js
+++ b/toolkit/components/aboutperformance/content/aboutPerformance.js
@@ -564,17 +564,17 @@ var View = {
     subset = subset.slice().sort(Delta.revCompare);
 
     let watcherAlerts = null;
     if (nature == "addons") {
       watcherAlerts = AddonWatcher.alerts;
     }
 
     // Grab everything from the DOM before cleaning up
-    let eltContainer = this._setupStructure(id);
+    this._setupStructure(id);
 
     // An array of `cachedElements` that need to be added
     let toAdd = [];
     for (let delta of subset) {
       if (!(delta instanceof Delta)) {
         throw new TypeError();
       }
       let cachedElements = this._grabOrCreateElements(delta, nature);
@@ -644,17 +644,16 @@ var View = {
             }
 
             eltImpact.textContent = ` ${describeFrequency} ${describeImpact}`;
             cachedElements.eltFPS.textContent = `Impact on framerate: ${delta.alerts[1] || 0} high-impacts, ${delta.alerts[0] || 0} medium-impact${jankSuffix}.`;
           }
           cachedElements.eltRoot.setAttribute("impact", Math.round(impact));
         }
 
-        let result = delta.diff.jank.totalCPUTime/delta.diff.deltaT;
         cachedElements.eltCPU.textContent = `CPU usage: ${Math.ceil(delta.diff.jank.totalCPUTime/delta.diff.deltaT/10)}% (total ${delta.diff.jank.totalUserTime}ms).`;
         cachedElements.eltSystem.textContent = `System usage: ${Math.ceil(delta.diff.jank.totalSystemTime/delta.diff.deltaT/10)}% (total ${delta.diff.jank.totalSystemTime}ms).`;
         cachedElements.eltCPOW.textContent = `Blocking process calls: ${Math.ceil(delta.diff.cpow.totalCPOWTime/delta.diff.deltaT/10)}% (total ${delta.diff.cpow.totalCPOWTime}ms).`;
       }
     }
     this._insertElements(toAdd, id);
   },
 

--- a/toolkit/components/aboutperformance/tests/browser/browser_aboutperformance.js
+++ b/toolkit/components/aboutperformance/tests/browser/browser_aboutperformance.js
@@ -63,17 +63,16 @@ function frameScript() {
     Services.obs.notifyObservers(null, "test-about:performance-test-driver", JSON.stringify(options));
   });
 
   addMessageListener("aboutperformance-test:checkSanity", ({data: options}) => {
     let exn = null;
     try {
       let reFullname = /Full name: (.+)/;
       let reFps = /Impact on framerate: (\d+)\/10( \((\d+) alerts\))?/;
-      let reCpu = /CPU usage: (\d+)%/
       let reCpow = /Blocking process calls: (\d+)%( \((\d+) alerts\))?/;
 
       let getContentOfSelector = function(eltContainer, selector, re) {
         let elt = eltContainer.querySelector(selector);
         if (!elt) {
           throw new Error(`No item ${selector}`);
         }
 

--- a/toolkit/components/addoncompat/Prefetcher.jsm
+++ b/toolkit/components/addoncompat/Prefetcher.jsm
@@ -158,17 +158,17 @@ PropertyOp.prototype.addObject = functio
   database.cache(this.index, obj, has, propValue);
   if (has && !isPrimitive(propValue) && this.outputTable) {
     database.add(this.outputTable, propValue);
   }
 }
 
 PropertyOp.prototype.makeCacheEntry = function(item, cache)
 {
-  let [index, obj, has, propValue] = item;
+  let [, obj, , propValue] = item;
 
   let desc = { configurable: false, enumerable: true, writable: false, value: propValue };
 
   if (!cache.has(obj)) {
     cache.set(obj, new Map());
   }
   let propMap = cache.get(obj);
   propMap.set(this.prop, desc);
@@ -196,17 +196,17 @@ MethodOp.prototype.addObject = function(
   database.cache(this.index, obj, result);
   if (!isPrimitive(result) && this.outputTable) {
     database.add(this.outputTable, result);
   }
 }
 
 MethodOp.prototype.makeCacheEntry = function(item, cache)
 {
-  let [index, obj, result] = item;
+  let [, obj, result] = item;
 
   if (!cache.has(obj)) {
     cache.set(obj, new Map());
   }
   let propMap = cache.get(obj);
   let fallback = propMap.get(this.method);
 
   let method = this.method;
@@ -251,17 +251,17 @@ CollectionOp.prototype.addObject = funct
     if (!isPrimitive(elements[i]) && this.outputTable) {
       database.add(this.outputTable, elements[i]);
     }
   }
 }
 
 CollectionOp.prototype.makeCacheEntry = function(item, cache)
 {
-  let [index, obj, ...elements] = item;
+  let [, obj, ...elements] = item;
 
   if (!cache.has(obj)) {
     cache.set(obj, new Map());
   }
   let propMap = cache.get(obj);
 
   let lenDesc = { configurable: false, enumerable: true, writable: false, value: elements.length };
   propMap.set("length", lenDesc);

--- a/toolkit/components/addoncompat/multiprocessShims.js
+++ b/toolkit/components/addoncompat/multiprocessShims.js
@@ -108,17 +108,16 @@ AddonInterpositionService.prototype = {
 
   // When the interface is not known for a method call, this code
   // determines the type of the target object.
   getObjectTag: function(target) {
     if (Cu.isCrossProcessWrapper(target)) {
       return Cu.getCrossProcessWrapperTag(target);
     }
 
-    const XUL_NS = "http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul";
     if (target instanceof Ci.nsIDOMXULElement) {
       if (target.localName == "browser" && target.isRemoteBrowser) {
         return "RemoteBrowserElement";
       }
 
       if (target.localName == "tabbrowser") {
         return "TabBrowserElement";
       }

--- a/toolkit/components/alerts/test/test_alerts_requireinteraction.html
+++ b/toolkit/components/alerts/test/test_alerts_requireinteraction.html
@@ -93,17 +93,16 @@ add_task(function* test_require_interact
     "first finished",
     "third replacement show",
     "second replacement finished",
     "third replacement finished"
   ];
 
   var actualSequence = [];
 
-  var sequenceIdx = 0;
   function createAlertListener(name, showCallback, finishCallback) {
     return (subject, topic, data) => {
       if (topic == "alertshow") {
         actualSequence.push(name + " show");
         if (showCallback) {
           showCallback();
         }
       } else if (topic == "alertfinished") {

--- a/toolkit/components/alerts/test/test_image.html
+++ b/toolkit/components/alerts/test/test_image.html
@@ -46,17 +46,17 @@ function promiseImage(alert, timeout = 0
 }
 
 add_task(function* testContext() {
   var inUserData = Cc["@mozilla.org/supports-PRInt64;1"]
                      .createInstance(Ci.nsISupportsPRInt64);
   inUserData.data = 123;
 
   var alert = makeAlert(null, imageServerURL + "?f=image.png");
-  var [ready, request, userData] = yield promiseImage(alert, 0, inUserData);
+  var [ready, , userData] = yield promiseImage(alert, 0, inUserData);
   ok(ready, "Should load requested image");
   is(userData.QueryInterface(Ci.nsISupportsPRInt64).data, 123,
      "Should pass user data for loaded image");
 
   alert = makeAlert(null, imageServerURL + "?s=404");
   [ready, userData] = yield promiseImage(alert, 0, inUserData);
   ok(!ready, "Should not load missing image");
   is(userData.QueryInterface(Ci.nsISupportsPRInt64).data, 123,

--- a/toolkit/components/asyncshutdown/AsyncShutdown.jsm
+++ b/toolkit/components/asyncshutdown/AsyncShutdown.jsm
@@ -520,17 +520,16 @@ Spinner.prototype = {
   get name() {
     return this._barrier.client.name;
   },
 
   // nsIObserver.observe
   observe: function() {
     let topic = this._topic;
     debug(`Starting phase ${ topic }`);
-    let barrier = this._barrier;
     Services.obs.removeObserver(this, topic);
 
     let satisfied = false; // |true| once we have satisfied all conditions
     let promise;
     try {
       promise = this._barrier.wait({
         warnAfterMS: DELAY_WARNING_MS,
         crashAfterMS: DELAY_CRASH_MS

--- a/toolkit/components/autocomplete/tests/unit/test_immediate_search.js
+++ b/toolkit/components/autocomplete/tests/unit/test_immediate_search.js
@@ -30,17 +30,16 @@ AutoCompleteResult.prototype = Object.cr
 function run_test() {
   run_next_test();
 }
 
 /**
  * An immediate search should be executed synchronously.
  */
 add_test(function test_immediate_search() {
-  let immediateResults = ["mozillaTest"];
   let inputStr = "moz";
 
   let immediateSearch = new AutoCompleteImmediateSearch(
     "immediate", new AutoCompleteResult(["moz-immediate"], 0));
   registerAutoCompleteSearch(immediateSearch);
   let delayedSearch = new AutoCompleteDelayedSearch(
     "delayed", new AutoCompleteResult(["moz-delayed"], 0));
   registerAutoCompleteSearch(delayedSearch);
@@ -74,17 +73,16 @@ add_test(function test_immediate_search(
     run_next_test();
   };
 });
 
 /**
  * An immediate search should be executed before any delayed search.
  */
 add_test(function test_immediate_search_notimeout() {
-  let immediateResults = ["mozillaTest"];
   let inputStr = "moz";
 
   let immediateSearch = new AutoCompleteImmediateSearch(
     "immediate", new AutoCompleteResult(["moz-immediate"], 0));
   registerAutoCompleteSearch(immediateSearch);
 
   let delayedSearch = new AutoCompleteDelayedSearch(
     "delayed", new AutoCompleteResult(["moz-delayed"], 0));
@@ -119,17 +117,16 @@ add_test(function test_immediate_search_
   unregisterAutoCompleteSearch(delayedSearch);
   run_next_test();
 });
 
 /**
  * A delayed search should be executed synchronously with a zero timeout.
  */
 add_test(function test_delayed_search_notimeout() {
-  let immediateResults = ["mozillaTest"];
   let inputStr = "moz";
 
   let delayedSearch = new AutoCompleteDelayedSearch(
     "delayed", new AutoCompleteResult(["moz-delayed"], 0));
   registerAutoCompleteSearch(delayedSearch);
 
   let controller = Cc["@mozilla.org/autocomplete/controller;1"].
                    getService(Ci.nsIAutoCompleteController);

--- a/toolkit/components/autocomplete/tests/unit/test_previousResult.js
+++ b/toolkit/components/autocomplete/tests/unit/test_previousResult.js
@@ -238,17 +238,16 @@ function run_test() {
   var controller = Components.classes["@mozilla.org/autocomplete/controller;1"].
                    getService(Components.interfaces.nsIAutoCompleteController);
 
   // Make an AutoCompleteInput that uses our search
   // and confirms results on search complete
   var input = new AutoCompleteInput([search1.name,
                                      search2.name]);
   var numSearchesStarted = 0;
-  var previousResult = null;
 
   input.onSearchBegin = function() {
     numSearchesStarted++;
   };
 
   input.onSearchComplete = function() {
     do_check_eq(controller.searchStatus,
                 Ci.nsIAutoCompleteController.STATUS_COMPLETE_MATCH);
@@ -274,9 +273,8 @@ function run_test() {
 
   controller.input = input;
 
   // Search is asynchronous, so don't let the test finish immediately
   do_test_pending();
 
   controller.startSearch("test");
 }
-

--- a/toolkit/components/cookie/content/cookieAcceptDialog.js
+++ b/toolkit/components/cookie/content/cookieAcceptDialog.js
@@ -54,17 +54,16 @@ function onload()
   } else {
     document.getElementById('disclosureButton').setAttribute("label", hideDetails);
   }
   document.getElementById('disclosureButton').setAttribute("accesskey", detailsAccessKey);
 
   if ("arguments" in window && window.arguments.length >= 1 && window.arguments[0]) {
     try {
       params = window.arguments[0].QueryInterface(nsIDialogParamBlock);
-      var objects = params.objects;
       var cookie = params.objects.queryElementAt(0, nsICookie);
       var cookiesFromHost = params.GetInt(nsICookieAcceptDialog.COOKIESFROMHOST);
 
       var messageFormat;
       if (params.GetInt(nsICookieAcceptDialog.CHANGINGCOOKIE))
         messageFormat = 'permissionToModifyCookie';
       else if (cookiesFromHost > 1)
         messageFormat = 'permissionToSetAnotherCookie';

--- a/toolkit/components/crashes/CrashManager.jsm
+++ b/toolkit/components/crashes/CrashManager.jsm
@@ -1038,17 +1038,17 @@ CrashStore.prototype = Object.freeze({
 
   /**
    * All crashes tracked.
    *
    * This is an array of CrashRecord.
    */
   get crashes() {
     let crashes = [];
-    for (let [id, crash] of this._data.crashes) {
+    for (let [, crash] of this._data.crashes) {
       crashes.push(new CrashRecord(crash));
     }
 
     return crashes;
   },
 
   /**
    * Obtain a particular crash from its ID.

--- a/toolkit/components/crashes/CrashService.js
+++ b/toolkit/components/crashes/CrashService.js
@@ -57,15 +57,15 @@ CrashService.prototype = Object.freeze({
 
     Services.crashmanager.addCrash(processType, crashType, id, new Date());
   },
 
   observe: function (subject, topic, data) {
     switch (topic) {
       case "profile-after-change":
         // Side-effect is the singleton is instantiated.
-        let m = Services.crashmanager;
+        Services.crashmanager;
         break;
     }
   },
 });
 
 this.NSGetFactory = XPCOMUtils.generateNSGetFactory([CrashService]);

--- a/toolkit/components/ctypes/tests/unit/test_finalizer_shouldfail.js
+++ b/toolkit/components/ctypes/tests/unit/test_finalizer_shouldfail.js
@@ -108,17 +108,17 @@ function test_double_dispose() {
  * Test that nothing (too) bad happens when the finalizer is NULL
  */
 function test_null_dispose()
 {
   let exception;
 
   exception = false;
   try {
-    let v = ctypes.CDataFinalizer(acquire(0), null_dispose);
+    ctypes.CDataFinalizer(acquire(0), null_dispose);
   } catch (x) {
     exception = true;
   }
   do_check_true(exception);
 }
 
 /**
  * Test that conversion of a disposed/forgotten CDataFinalizer to a C

--- a/toolkit/components/ctypes/tests/unit/test_jsctypes.js
+++ b/toolkit/components/ctypes/tests/unit/test_jsctypes.js
@@ -1432,17 +1432,16 @@ function run_StructType_tests() {
 
   do_check_eq(g_t.toString(), "type " + name);
   do_check_eq(g_t.toSource(),
     "ctypes.StructType(\"g_t\", [{ \"a\": ctypes.int32_t }, { \"b\": ctypes.double }])");
   do_check_true(g_t.ptr === ctypes.PointerType(g_t));
   do_check_eq(g_t.array().name, name + "[]");
   do_check_eq(g_t.array(5).name, name + "[5]");
 
-  let h_t = ctypes.StructType("h_t", [{ a: ctypes.int32_t }, { b: ctypes.int16_t }]);
   let s_t = new ctypes.StructType("s_t", [{ a: ctypes.int32_t }, { b: g_t }, { c: ctypes.int8_t }]);
 
   let fields = [{ a: ctypes.int32_t }, { b: ctypes.int8_t }, { c: g_t }, { d: ctypes.int8_t }];
   let t_t = new ctypes.StructType("t_t", fields);
   do_check_eq(t_t.fields.length, 4);
   do_check_true(t_t.fields[0].a === ctypes.int32_t);
   do_check_true(t_t.fields[1].b === ctypes.int8_t);
   do_check_true(t_t.fields[2].c === g_t);
@@ -1840,17 +1839,16 @@ function run_FunctionType_tests() {
   do_check_throws(function() {
     ctypes.FunctionType(ctypes.default_abi, ctypes.int32_t());
   }, TypeError);
   do_check_throws(function() {
     ctypes.FunctionType(ctypes.void_t, ctypes.void_t);
   }, Error);
 
   let g_t = ctypes.StructType("g_t", [{ a: ctypes.int32_t }, { b: ctypes.double }]);
-  let g = g_t(1, 2);
 
   let f_t = ctypes.FunctionType(ctypes.default_abi, g_t);
   let name = "g_t()";
   do_check_eq(f_t.name, name);
   do_check_eq(f_t.size, undefined);
   do_check_true(f_t.abi === ctypes.default_abi);
   do_check_true(f_t.returnType === g_t);
   do_check_true(f_t.argTypes.length == 0);
@@ -2167,29 +2165,27 @@ function run_cast_tests() {
   // Test casting to a type of undefined or larger size.
   do_check_throws(function() { ctypes.cast(i, ctypes.void_t); }, TypeError);
   do_check_throws(function() { ctypes.cast(i, ctypes.int32_t.array()); }, TypeError);
   do_check_throws(function() { ctypes.cast(i, ctypes.int64_t); }, TypeError);
 
   // Test casting between special types.
   let g_t = ctypes.StructType("g_t", [{ a: ctypes.int32_t }, { b: ctypes.double }]);
   let a_t = ctypes.ArrayType(g_t, 4);
-  let p_t = ctypes.PointerType(g_t);
   let f_t = ctypes.FunctionType(ctypes.default_abi, ctypes.void_t).ptr;
 
   let a = a_t();
   a[0] = { a: 5, b: 7.5 };
   let g = ctypes.cast(a, g_t);
   do_check_eq(ptrValue(a.address()), ptrValue(g.address()));
   do_check_eq(a[0].a, g.a);
 
   let a2 = ctypes.cast(g, g_t.array(1));
   do_check_eq(ptrValue(a2.address()), ptrValue(g.address()));
   do_check_eq(a2[0].a, g.a);
-  let a3 = ctypes.cast(g, g_t.array(0));
 
   let p = g.address();
   let ip = ctypes.cast(p, ctypes.int32_t.ptr);
   do_check_eq(ptrValue(ip), ptrValue(p));
   do_check_eq(ptrValue(ip.address()), ptrValue(p.address()));
   do_check_eq(ip.contents, g.a);
 
   let f = f_t(0x5);
@@ -2210,17 +2206,17 @@ function run_void_tests(library) {
   if ("winLastError" in ctypes) {
     test_void_t = library.declare("test_void_t_stdcall", ctypes.stdcall_abi, ctypes.void_t);
     do_check_eq(test_void_t(), undefined);
 
     // Check that WINAPI symbol lookup for a regular stdcall function fails on
     // Win32 (it's all the same on Win64 though).
     if (ctypes.voidptr_t.size == 4) {
       do_check_throws(function() {
-        let test_winapi_t = library.declare("test_void_t_stdcall", ctypes.winapi_abi, ctypes.void_t);
+        library.declare("test_void_t_stdcall", ctypes.winapi_abi, ctypes.void_t);
       }, Error);
     }
   }
 }
 
 function run_string_tests(library) {
   let test_ansi_len = library.declare("test_ansi_len", ctypes.default_abi, ctypes.int32_t, ctypes.char.ptr);
   do_check_eq(test_ansi_len(""), 0);

--- a/toolkit/components/downloads/test/unit/test_app_rep.js
+++ b/toolkit/components/downloads/test/unit/test_app_rep.js
@@ -182,18 +182,16 @@ add_test(function test_local_list() {
       for (let i = 0; i < gTables[table].length; ++i) {
         response += "u:" + gTables[table][i] + "\n";
       }
     }
     do_print("Returning update response: " + response);
     return response;
   }
   gHttpServ.registerPathHandler("/downloads", function(request, response) {
-    let buf = NetUtil.readInputStreamToString(request.bodyInputStream,
-      request.bodyInputStream.available());
     let blob = processUpdateRequest();
     response.setHeader("Content-Type",
                        "application/vnd.google.safebrowsing-update", false);
     response.setStatusLine(request.httpVersion, 200, "OK");
     response.bodyOutputStream.write(blob, blob.length);
   });
 
   let streamUpdater = Cc["@mozilla.org/url-classifier/streamupdater;1"]

--- a/toolkit/components/downloads/test/unit/test_app_rep_maclinux.js
+++ b/toolkit/components/downloads/test/unit/test_app_rep_maclinux.js
@@ -157,18 +157,16 @@ function processUpdateRequest() {
   do_print("Returning update response: " + response);
   return response;
 }
 
 // Set up the local whitelist.
 function waitForUpdates() {
   let deferred = Promise.defer();
   gHttpServer.registerPathHandler("/downloads", function(request, response) {
-    let buf = NetUtil.readInputStreamToString(request.bodyInputStream,
-      request.bodyInputStream.available());
     let blob = processUpdateRequest();
     response.setHeader("Content-Type",
                        "application/vnd.google.safebrowsing-update", false);
     response.setStatusLine(request.httpVersion, 200, "OK");
     response.bodyOutputStream.write(blob, blob.length);
   });
 
   let streamUpdater = Cc["@mozilla.org/url-classifier/streamupdater;1"]

--- a/toolkit/components/downloads/test/unit/test_app_rep_windows.js
+++ b/toolkit/components/downloads/test/unit/test_app_rep_windows.js
@@ -257,18 +257,16 @@ function processUpdateRequest() {
   do_print("Returning update response: " + response);
   return response;
 }
 
 // Set up the local whitelist.
 function waitForUpdates() {
   let deferred = Promise.defer();
   gHttpServer.registerPathHandler("/downloads", function(request, response) {
-    let buf = NetUtil.readInputStreamToString(request.bodyInputStream,
-      request.bodyInputStream.available());
     let blob = processUpdateRequest();
     response.setHeader("Content-Type",
                        "application/vnd.google.safebrowsing-update", false);
     response.setStatusLine(request.httpVersion, 200, "OK");
     response.bodyOutputStream.write(blob, blob.length);
   });
 
   let streamUpdater = Cc["@mozilla.org/url-classifier/streamupdater;1"]

--- a/toolkit/components/feeds/FeedProcessor.js
+++ b/toolkit/components/feeds/FeedProcessor.js
@@ -965,18 +965,16 @@ function ExtensionHandler(processor) {
 
 ExtensionHandler.prototype = {
   startDocument: function EH_startDocument() {
   },
   endDocument: function EH_endDocument() {
   },
   startElement: function EH_startElement(uri, localName, qName, attrs) {
     ++this._depth;
-    var prefix = gNamespaces[uri] ? gNamespaces[uri] + ":" : "";
-    var key =  prefix + localName;
 
     if (this._depth == 1) {
       this._uri = uri;
       this._localName = localName;
       this._qName = qName;
       this._attrs = attrs;
     }
 
@@ -1493,17 +1491,17 @@ FeedProcessor.prototype = {
   },
 
   // end of nsISAXContentHandler
 
   // Handle our more complicated elements--those that contain
   // attributes and child elements.
   _processComplexElement:
   function FP__processComplexElement(elementInfo, attributes) {
-    var obj, key, prefix;
+    var obj;
 
     // If the container is an entry/item, it'll need to have its
     // more esoteric properties put in the 'fields' property bag.
     if (elementInfo.containerClass == Cc[ENTRY_CONTRACTID]) {
       obj = elementInfo.containerClass.createInstance(Ci.nsIFeedEntry);
       obj.baseURI = this._xmlBaseStack[this._xmlBaseStack.length - 1];
       this._mapAttributes(obj.fields, attributes);
     }

--- a/toolkit/components/filepicker/content/filepicker.js
+++ b/toolkit/components/filepicker/content/filepicker.js
@@ -656,19 +656,17 @@ function newDir() {
       showErrorDialog("errorNewDirDoesExistTitle",
                       "errorNewDirDoesExistMessage",
                       file);
       return false;
     }
 
     var parent = file.parent;
     if (!(parent.exists() && parent.isDirectory() && parent.isWritable())) {
-      var oldParent = parent;
       while (!parent.exists()) {
-        oldParent = parent;
         parent = parent.parent;
       }
       if (parent.isFile()) {
         showErrorDialog("errorCreateNewDirTitle",
                         "errorCreateNewDirIsFileMessage",
                         parent);
         return false;
       }

--- a/toolkit/components/filepicker/nsFilePicker.js
+++ b/toolkit/components/filepicker/nsFilePicker.js
@@ -265,27 +265,16 @@ nsFilePicker.prototype = {
         var appShellService = Components.classes[APPSHELL_SERV_CONTRACTID].getService(nsIAppShellService);
         parent = appShellService.hiddenDOMWindow;
       } catch (ex) {
         debug("Can't get parent.  xpconnect hates me so we can't get one from the appShellService.\n");
         debug(ex + "\n");
       }
     }
 
-    var parentWin = null;
-    try {
-      parentWin = parent.QueryInterface(nsIInterfaceRequestor)
-                        .getInterface(nsIWebNavigation)
-                        .QueryInterface(nsIDocShellTreeItem)
-                        .treeOwner
-                        .QueryInterface(nsIInterfaceRequestor)
-                        .getInterface(nsIBaseWindow);
-    } catch (ex) {
-      dump("file picker couldn't get base window\n"+ex+"\n");
-    }
     try {
       parent.openDialog("chrome://global/content/filepicker.xul",
                         "",
                         "chrome,modal,titlebar,resizable=yes,dependent=yes",
                         o);
 
       this.mFilterIndex = o.retvals.filterIndex;
       this.mFilesEnumerator = o.retvals.files;
@@ -323,9 +312,8 @@ function srGetStrBundle(path)
   }
 
   strBundle = strBundleService.createBundle(path);
   if (!strBundle) {
 	dump("\n--** strBundle createInstance failed **--\n");
   }
   return strBundle;
 }
-

--- a/toolkit/components/gfx/SanityTest.js
+++ b/toolkit/components/gfx/SanityTest.js
@@ -175,17 +175,16 @@ var listener = {
     // Perform the compositor backbuffer test, which currently we use for
     // actually deciding whether to enable hardware media decoding.
     testCompositor(this.win, this.ctx);
 
     this.endTest();
   },
 
   receiveMessage(message) {
-    let data = message.data;
     switch (message.name) {
       case "gfxSanity:ContentLoaded":
         this.runSanityTest();
         break;
     }
   },
 
   onWindowLoaded: function() {
@@ -239,17 +238,16 @@ function SanityTest() {}
 SanityTest.prototype = {
   classID: Components.ID("{f3a8ca4d-4c83-456b-aee2-6a2cbf11e9bd}"),
   QueryInterface: XPCOMUtils.generateQI([Ci.nsIObserver,
                                          Ci.nsISupportsWeakReference]),
 
   shouldRunTest: function() {
     // Only test gfx features if firefox has updated, or if the user has a new
     // gpu or drivers.
-    var appInfo = Cc["@mozilla.org/xre/app-info;1"].getService(Ci.nsIXULAppInfo);
     var buildId = Services.appinfo.platformBuildID;
     var gfxinfo = Cc["@mozilla.org/gfx/info;1"].getService(Ci.nsIGfxInfo);
 
     if (Preferences.get(RUNNING_PREF, false)) {
       Preferences.set(DISABLE_VIDEO_PREF, true);
       reportResult(TEST_CRASHED);
       return false;
     }

--- a/toolkit/components/jsdownloads/test/unit/common_test_Download.js
+++ b/toolkit/components/jsdownloads/test/unit/common_test_Download.js
@@ -2375,21 +2375,21 @@ add_task(function* test_platform_integra
     targetFilePath = OS.Path.join(targetFilePath,
                                   "test" + (Math.floor(Math.random() * 1000000)));
     let targetFile = new FileUtils.File(targetFilePath);
     downloadFiles.push(targetFile);
 
     let download;
     if (gUseLegacySaver) {
       download = yield promiseStartLegacyDownload(httpUrl("source.txt"),
-                                                  { targetFile: targetFile });
+                                                  { isPrivate, targetFile });
     }
     else {
       download = yield Downloads.createDownload({
-        source: httpUrl("source.txt"),
+        source: { url: httpUrl("source.txt"), isPrivate },
         target: targetFile,
       });
       download.start().catch(() => {});
     }
 
     // Wait for the whenSucceeded promise to be resolved first.
     // downloadDone should be called before the whenSucceeded promise is resolved.
     yield download.whenSucceeded().then(function () {

--- a/toolkit/components/jsdownloads/test/unit/head.js
+++ b/toolkit/components/jsdownloads/test/unit/head.js
@@ -815,21 +815,16 @@ add_task(function test_common_initialize
       // We have to invalidate the previously computed directory path.
       this._downloadsDirectory = null;
     },
     _getDirectory(name) {
       return super._getDirectory(this._allowDirectories ? name : "TmpD");
     },
   }));
 
-  // Get a reference to nsIComponentRegistrar, and ensure that is is freed
-  // before the XPCOM shutdown.
-  let registrar = Components.manager.QueryInterface(Ci.nsIComponentRegistrar);
-  do_register_cleanup(() => registrar = null);
-
   // Make sure that downloads started using nsIExternalHelperAppService are
   // saved to disk without asking for a destination interactively.
   let mock = {
     QueryInterface: XPCOMUtils.generateQI([Ci.nsIHelperAppLauncherDialog]),
     promptForSaveToFileAsync(aLauncher,
                              aWindowContext,
                              aDefaultFileName,
                              aSuggestedFileExtension,

--- a/toolkit/components/jsdownloads/test/unit/test_DownloadIntegration.js
+++ b/toolkit/components/jsdownloads/test/unit/test_DownloadIntegration.js
@@ -403,17 +403,17 @@ add_task(function* test_suspend_resume()
 add_task(function* test_exit_private_browsing()
 {
   mustInterruptResponses();
 
   let privateList = yield promiseNewList(true);
   let download1 = yield promiseNewDownload(httpUrl("source.txt"));
   let download2 = yield promiseNewDownload(httpUrl("interruptible.txt"));
   let promiseAttempt1 = download1.start();
-  let promiseAttempt2 = download2.start();
+  download2.start();
 
   // Add downloads to list.
   yield privateList.add(download1);
   yield privateList.add(download2);
 
   // Complete the download.
   yield promiseAttempt1;
 

--- a/toolkit/components/jsdownloads/test/unit/test_DownloadStore.js
+++ b/toolkit/components/jsdownloads/test/unit/test_DownloadStore.js
@@ -106,17 +106,17 @@ add_task(function* test_save_reload()
   }
 });
 
 /**
  * Checks that saving an empty list deletes any existing file.
  */
 add_task(function* test_save_empty()
 {
-  let [list, store] = yield promiseNewListAndStore();
+  let [, store] = yield promiseNewListAndStore();
 
   let createdFile = yield OS.File.open(store.path, { create: true });
   yield createdFile.close();
 
   yield store.save();
 
   do_check_false(yield OS.File.exists(store.path));
 

--- a/toolkit/components/mediasniffer/test/unit/test_mediasniffer_ext.js
+++ b/toolkit/components/mediasniffer/test/unit/test_mediasniffer_ext.js
@@ -51,17 +51,17 @@ var listener = {
     do_check_eq(request.QueryInterface(Ci.nsIChannel).contentType, tests[testRan].expected);
   },
 
   onDataAvailable: function(request, context, stream, offset, count) {
     try {
       var bis = Components.classes["@mozilla.org/binaryinputstream;1"]
                           .createInstance(Components.interfaces.nsIBinaryInputStream);
       bis.setInputStream(stream);
-      var array = bis.readByteArray(bis.available());
+      bis.readByteArray(bis.available());
     } catch (ex) {
       do_throw("Error in onDataAvailable: " + ex);
     }
   },
 
   onStopRequest: function(request, context, status) {
     testRan++;
     runNext();
@@ -83,17 +83,16 @@ function runNext() {
     do_test_finished();
     return;
   }
   var channel = setupChannel("/");
   channel.asyncOpen2(listener);
 }
 
 function getFileContents(aFile) {
-  const PR_RDONLY = 0x01;
   var fileStream = Cc["@mozilla.org/network/file-input-stream;1"]
                       .createInstance(Ci.nsIFileInputStream);
   fileStream.init(aFile, 1, -1, null);
   var bis = Components.classes["@mozilla.org/binaryinputstream;1"]
                       .createInstance(Components.interfaces.nsIBinaryInputStream);
   bis.setInputStream(fileStream);
 
   var data = bis.readByteArray(bis.available());

--- a/toolkit/components/perfmonitoring/tests/browser/browser_AddonWatcher.js
+++ b/toolkit/components/perfmonitoring/tests/browser/browser_AddonWatcher.js
@@ -36,25 +36,16 @@ add_task(function* init() {
 
   yield ready;
 
   registerCleanupFunction(() => {
     info("Uninstalling test add-on");
     addon.uninstall()
   });
 
-
-  let freezeThreshold = Preferences.get("browser.addon-watch.freeze-threshold-micros", /* 5 seconds */ 5000000);
-  let jankThreshold = Preferences.get("browser.addon-watch.jank-threshold-micros", /* 256 ms == 8 frames*/ 256000);
-  let occurrencesBetweenAlerts = Preferences.get("browser.addon-watch.occurrences-between-alerts", 3);
-  let delayBetweenAlerts = Preferences.get("browser.addon-watch.delay-between-alerts-ms", 6 * 3600 * 1000 /* 6h */);
-  let delayBetweenFreezeAlerts = Preferences.get("browser.addon-watch.delay-between-freeze-alerts-ms", 2 * 60 * 1000 /* 2 min */);
-  let prescriptionDelay = Preferences.get("browser.addon-watch.prescription-delay", 5 * 60 * 1000 /* 5 minutes */);
-  let highestNumberOfAddonsToReport = Preferences.get("browser.addon-watch.max-simultaneous-reports", 1);
-
   Preferences.set("browser.addon-watch.warmup-ms", 0);
   Preferences.set("browser.addon-watch.freeze-threshold-micros", 0);
   Preferences.set("browser.addon-watch.jank-threshold-micros", 0);
   Preferences.set("browser.addon-watch.occurrences-between-alerts", 0);
   Preferences.set("browser.addon-watch.delay-between-alerts-ms", 0);
   Preferences.set("browser.addon-watch.delay-between-freeze-alerts-ms", 0);
   Preferences.set("browser.addon-watch.max-simultaneous-reports", 10000);
   Preferences.set("browser.addon-watch.deactivate-after-idle-ms", 100000000);

--- a/toolkit/components/perfmonitoring/tests/browser/browser_compartments.js
+++ b/toolkit/components/perfmonitoring/tests/browser/browser_compartments.js
@@ -22,19 +22,16 @@ const PARENT_PID = Services.appinfo.proc
 // This function is injected as source as a frameScript
 function frameScript() {
   try {
     "use strict";
 
     const { utils: Cu, classes: Cc, interfaces: Ci } = Components;
     Cu.import("resource://gre/modules/PerformanceStats.jsm");
     Cu.import("resource://gre/modules/Services.jsm");
-    let performanceStatsService =
-      Cc["@mozilla.org/toolkit/performance-stats-service;1"].
-      getService(Ci.nsIPerformanceStatsService);
 
     // Make sure that the stopwatch is now active.
     let monitor = PerformanceStats.getMonitor(["jank", "cpow", "ticks", "compartments"]);
 
     addMessageListener("compartments-test:getStatistics", () => {
       try {
         monitor.promiseSnapshot().then(snapshot => {
           sendAsyncMessage("compartments-test:getStatistics", {snapshot, pid: Services.appinfo.processID});

--- a/toolkit/components/printing/content/printjoboptions.js
+++ b/toolkit/components/printing/content/printjoboptions.js
@@ -130,18 +130,16 @@ paperListElement.prototype =
 // ---------------------------------------------------
 function createPaperArrayFromDefaults()
 {
   var paperNames   = ["letterSize", "legalSize", "exectiveSize", "a5Size", "a4Size", "a3Size", "a2Size", "a1Size", "a0Size"];
   // var paperNames   = ["&letterRadio.label;", "&legalRadio.label;", "&exectiveRadio.label;", "&a4Radio.label;", "&a3Radio.label;"];
   var paperWidths  = [ 8.5,  8.5,  7.25, 148.0, 210.0, 287.0, 420.0, 594.0,  841.0];
   var paperHeights = [11.0, 14.0, 10.50, 210.0, 297.0, 420.0, 594.0, 841.0, 1189.0];
   var paperInches  = [true, true, true,  false, false, false, false, false, false];
-  // this is deprecated
-  var paperEnums  = [0, 1, 2, 3, 4, 5, 6, 7, 8];
 
   gPaperArray = new Array();
 
   for (var i=0;i<paperNames.length;i++) {
     var obj    = {};
     obj.name   = paperNames[i];
     obj.width  = paperWidths[i];
     obj.height = paperHeights[i];

--- a/toolkit/components/promiseworker/PromiseWorker.jsm
+++ b/toolkit/components/promiseworker/PromiseWorker.jsm
@@ -300,24 +300,22 @@ this.BasePromiseWorker.prototype = {
         throw ex;
       }
 
       let deferred = Promise.defer();
       this._queue.push({deferred:deferred, closure: closure, id: id});
       this.log("Message posted");
 
       let reply;
-      let isError = false;
       try {
         this.log("Expecting reply");
         reply = yield deferred.promise;
       } catch (error) {
         this.log("Got error", error);
         reply = error;
-        isError = true;
 
         if (error instanceof WorkerError) {
           // We know how to deserialize most well-known errors
           throw this.ExceptionHandlers[error.data.exn](error.data);
         }
 
         if (error instanceof ErrorEvent) {
           // Other errors get propagated as instances of ErrorEvent

--- a/toolkit/components/prompts/content/selectDialog.js
+++ b/toolkit/components/prompts/content/selectDialog.js
@@ -51,17 +51,16 @@ function dialogOnLoad() {
     try {
         Cc["@mozilla.org/sound;1"].
         createInstance(Ci.nsISound).
         playEventSound(Ci.nsISound.EVENT_SELECT_DIALOG_OPEN);
     } catch (e) { }
 }
 
 function dialogOK() {
-    let selected = listBox.selectedIndex;
     gArgs.setProperty("selected", listBox.selectedIndex);
     gArgs.setProperty("ok", true);
     return true;
 }
 
 function dialogDoubleClick() {
     dialogOK();
     window.close();

--- a/toolkit/components/prompts/content/tabprompts.xml
+++ b/toolkit/components/prompts/content/tabprompts.xml
@@ -295,17 +295,16 @@
             <body>
             <![CDATA[
                 if (event.defaultPrevented)
                     return;
 
                 event.stopPropagation();
                 if (action == "default") {
                     let bnum = this.args.defaultButtonNum || 0;
-                    let button = this.ui["button" + bnum];
                     this.onButtonClick(bnum);
                 } else { // action == "cancel"
                     this.onButtonClick(1); // Cancel button
                 }
             ]]>
             </body>
         </method>
     </implementation>

--- a/toolkit/components/satchel/FormHistory.jsm
+++ b/toolkit/components/satchel/FormHistory.jsm
@@ -777,17 +777,16 @@ this.FormHistory = {
     // if no terms selected, select everything
     aSelectTerms = (aSelectTerms) ?  aSelectTerms : validFields;
     validateSearchData(aSearchData, "Search");
 
     let stmt = makeSearchStatement(aSearchData, aSelectTerms);
 
     let handlers = {
       handleResult : function(aResultSet) {
-        let formHistoryFields = dbSchema.tables.moz_formhistory;
         for (let row = aResultSet.getNextRow(); row; row = aResultSet.getNextRow()) {
           let result = {};
           for (let field of aSelectTerms) {
             result[field] = row.getResultByName(field);
           }
 
           if (aCallbacks && aCallbacks.handleResult) {
             aCallbacks.handleResult(result);

--- a/toolkit/components/satchel/nsFormHistory.js
+++ b/toolkit/components/satchel/nsFormHistory.js
@@ -298,17 +298,17 @@ FormHistory.prototype = {
             if (stmt) {
                 stmt.reset();
             }
         }
     },
 
     entryExists : function entryExists(name, value) {
         this.log("entryExists for " + name + "=" + value);
-        let [id, guid] = this.getExistingEntryID(name, value);
+        let [id] = this.getExistingEntryID(name, value);
         this.log("entryExists: id=" + id);
         return (id != -1);
     },
 
     removeEntriesByTimeframe : function removeEntriesByTimeframe(beginTime, endTime) {
         this.log("removeEntriesByTimeframe for " + beginTime + " to " + endTime);
 
         this.sendIntNotification("before-removeEntriesByTimeframe", beginTime, endTime);

--- a/toolkit/components/satchel/test/test_bug_511615.html
+++ b/toolkit/components/satchel/test/test_bug_511615.html
@@ -69,17 +69,17 @@ function checkSelectedIndexAfterResponse
   }).then(popupState => {
     is(popupState.open, true, "Popup should still be open.");
     is(popupState.selectedIndex, expectedIndex, "Selected index should match.");
   });
 }
 
 function doKeyUnprivileged(key) {
   let keyName = "DOM_VK_" + key.toUpperCase();
-  let keycode, charcode, alwaysVal;
+  let keycode, charcode;
 
   if (key.length == 1) {
       keycode = 0;
       charcode = key.charCodeAt(0);
       alwaysval = charcode;
   } else {
       keycode = KeyEvent[keyName];
       if (!keycode)

--- a/toolkit/components/satchel/test/unit/test_notify.js
+++ b/toolkit/components/satchel/test/unit/test_notify.js
@@ -49,18 +49,16 @@ function next_test()
 function* run_test_steps() {
 
 try {
 
 var testnum = 0;
 var testdesc = "Setup of test form history entries";
 
 var entry1 = ["entry1", "value1"];
-var entry2 = ["entry2", "value2"];
-
 
 /* ========== 1 ========== */
 testnum = 1;
 testdesc = "Initial connection to storage module"
 
 yield updateEntry("remove", null, null, next_test);
 yield countEntries(null, null, function (num) { do_check_false(num, "Checking initial DB is empty"); next_test(); });
 

--- a/toolkit/components/search/tests/xpcshell/head_search.js
+++ b/toolkit/components/search/tests/xpcshell/head_search.js
@@ -54,18 +54,16 @@ function dumpn(text)
 }
 
 /**
  * Configure preferences to load engines from
  * chrome://testsearchplugin/locale/searchplugins/
  */
 function configureToLoadJarEngines()
 {
-  let defaultBranch = Services.prefs.getDefaultBranch(null);
-
   let url = "chrome://testsearchplugin/locale/searchplugins/";
   let resProt = Services.io.getProtocolHandler("resource")
                         .QueryInterface(Ci.nsIResProtocolHandler);
   resProt.setSubstitution("search-plugins",
                           Services.io.newURI(url, null, null));
 
   // Ensure a test engine exists in the app dir anyway.
   let dir = Services.dirsvc.get(NS_APP_SEARCH_DIR, Ci.nsIFile);

--- a/toolkit/components/search/tests/xpcshell/test_identifiers.js
+++ b/toolkit/components/search/tests/xpcshell/test_identifiers.js
@@ -26,17 +26,17 @@ add_test(function test_identifier() {
   engineFile.append("searchplugins");
   engineFile.append("test-search-engine.xml");
   engineFile.parent.create(Ci.nsIFile.DIRECTORY_TYPE, FileUtils.PERMS_DIRECTORY);
 
   // Copy the test engine to the test profile.
   let engineTemplateFile = do_get_file("data/engine.xml");
   engineTemplateFile.copyTo(engineFile.parent, "test-search-engine.xml");
 
-  let search = Services.search.init(function initComplete(aResult) {
+  Services.search.init(function initComplete(aResult) {
     do_print("init'd search service");
     do_check_true(Components.isSuccessCode(aResult));
 
     let profileEngine = Services.search.getEngineByName("Test search engine");
     let jarEngine = Services.search.getEngineByName("bug645970");
 
     do_check_true(profileEngine instanceof Ci.nsISearchEngine);
     do_check_true(jarEngine instanceof Ci.nsISearchEngine);

--- a/toolkit/components/search/tests/xpcshell/test_json_cache.js
+++ b/toolkit/components/search/tests/xpcshell/test_json_cache.js
@@ -53,17 +53,16 @@ function run_test() {
   let engineTemplateFile = do_get_file("data/engine.xml");
   engineTemplateFile.copyTo(engineFile.parent, "test-search-engine.xml");
 
   // The list of visibleDefaultEngines needs to match or the cache will be ignored.
   let chan = NetUtil.newChannel({
     uri: "resource://search-plugins/list.json",
     loadUsingSystemPrincipal: true
   });
-  let visibleDefaultEngines = [];
   let sis = Cc["@mozilla.org/scriptableinputstream;1"].
               createInstance(Ci.nsIScriptableInputStream);
   sis.init(chan.open2());
   let list = sis.read(sis.available());
   let searchSettings = JSON.parse(list);
 
   cacheTemplate.visibleDefaultEngines = searchSettings["default"]["visibleDefaultEngines"];
 
@@ -78,17 +77,17 @@ add_test(function prepare_test_data() {
 });
 
 /**
  * Start the search service and confirm the engine properties match the expected values.
  */
 add_test(function test_cached_engine_properties() {
   do_print("init search service");
 
-  let search = Services.search.init(function initComplete(aResult) {
+  Services.search.init(function initComplete(aResult) {
     do_print("init'd search service");
     do_check_true(Components.isSuccessCode(aResult));
 
     let engines = Services.search.getEngines({});
     let engine = engines[0];
 
     do_check_true(engine instanceof Ci.nsISearchEngine);
     isSubObjectOf(EXPECTED_ENGINE.engine, engine);

--- a/toolkit/components/search/tests/xpcshell/test_location_sync.js
+++ b/toolkit/components/search/tests/xpcshell/test_location_sync.js
@@ -50,17 +50,17 @@ add_task(function* test_simple() {
 
   ok(!Services.search.isInitialized);
 
   // setup a console listener for the timezone fallback message.
   let promiseTzMessage = promiseTimezoneMessage();
 
   // fetching the engines forces a sync init, and should have caused us to
   // check the timezone.
-  let engines = Services.search.getEngines();
+  Services.search.getEngines();
   ok(Services.search.isInitialized);
 
   // a little wait to check we didn't do the xhr thang.
   yield new Promise(resolve => {
     do_timeout(500, resolve);
   });
 
   let msg = yield promiseTzMessage;

--- a/toolkit/components/search/tests/xpcshell/test_sync_migration.js
+++ b/toolkit/components/search/tests/xpcshell/test_sync_migration.js
@@ -10,17 +10,17 @@ function run_test() {
 
   do_get_file("data/metadata.json").copyTo(gProfD, "search-metadata.json");
 
   run_next_test();
 }
 
 add_task(function* test_sync_metadata_migration() {
   do_check_false(Services.search.isInitialized);
-  let engines = Services.search.getEngines();
+  Services.search.getEngines();
   do_check_true(Services.search.isInitialized);
   yield promiseAfterCache();
 
   // Check that the entries are placed as specified correctly
   let metadata = yield promiseEngineMetadata();
   do_check_eq(metadata["engine"].order, 1);
   do_check_eq(metadata["engine"].alias, "foo");
 

--- a/toolkit/components/telemetry/tests/unit/test_ChildHistograms.js
+++ b/toolkit/components/telemetry/tests/unit/test_ChildHistograms.js
@@ -80,17 +80,17 @@ add_task(function*() {
   Services.prefs.setBoolPref(PREF_TELEMETRY_ENABLED, true);
   yield TelemetryController.testSetup();
   if (runningInParent) {
     // Make sure we don't generate unexpected pings due to pref changes.
     yield setEmptyPrefWatchlist();
   }
 
   // Run test in child, don't wait for it to finish.
-  let childPromise = run_test_in_child("test_ChildHistograms.js");
+  run_test_in_child("test_ChildHistograms.js");
   yield do_await_remote_message(MESSAGE_CHILD_TEST_DONE);
 
   yield ContentTaskUtils.waitForCondition(() => {
     let payload = TelemetrySession.getPayload("test-ping");
     return payload &&
            "processes" in payload &&
            "content" in payload.processes &&
            "histograms" in payload.processes.content &&

--- a/toolkit/components/telemetry/tests/unit/test_PingAPI.js
+++ b/toolkit/components/telemetry/tests/unit/test_PingAPI.js
@@ -101,17 +101,16 @@ add_task(function* test_archivedPings() 
       id: data.id,
       type: data.type,
       timestampCreated: data.dateCreated.getTime(),
     });
     Assert.deepEqual(list, expectedPingList, "Archived ping list should contain submitted pings");
   }
 
   // Check loading the archived pings.
-  let ids = PINGS.map(p => p.id);
   let checkLoadingPings = Task.async(function*() {
     for (let data of PINGS) {
       let ping = yield TelemetryArchive.promiseArchivedPingById(data.id);
       Assert.equal(ping.id, data.id, "Archived ping should have matching id");
       Assert.equal(ping.type, data.type, "Archived ping should have matching type");
       Assert.equal(ping.creationDate, data.dateCreated.toISOString(),
                    "Archived ping should have matching creation date");
     }
@@ -258,17 +257,17 @@ add_task(function* test_archiveCleanup()
   // We expect all the pings we archived to be in this histogram.
   h = Telemetry.getHistogramById("TELEMETRY_ARCHIVE_SESSION_PING_COUNT");
   Assert.equal(h.snapshot().sum, 22, "All the pings must be live-accumulated in the histogram.");
   // Reset the histogram that will be populated by the archive scan.
   Telemetry.getHistogramById("TELEMETRY_ARCHIVE_EVICTED_OLD_DIRS").clear();
   Telemetry.getHistogramById("TELEMETRY_ARCHIVE_OLDEST_DIRECTORY_AGE").clear();
 
   // Move the current date 60 days ahead of the first ping.
-  let now = fakeNow(futureDate(firstDate, 60 * MILLISECONDS_PER_DAY));
+  fakeNow(futureDate(firstDate, 60 * MILLISECONDS_PER_DAY));
   // Reset TelemetryArchive and TelemetryController to start the startup cleanup.
   yield TelemetryController.testReset();
   // Wait for the cleanup to finish.
   yield TelemetryStorage.testCleanupTaskPromise();
   // Then scan the archived dir.
   yield TelemetryArchive.promiseArchivedPingList();
 
   // Check that the archive is in the correct state.

--- a/toolkit/components/telemetry/tests/unit/test_TelemetryController.js
+++ b/toolkit/components/telemetry/tests/unit/test_TelemetryController.js
@@ -282,19 +282,16 @@ add_task(function* test_pingHasEnvironme
 
   // Test a field in the environment build section.
   Assert.equal(ping.application.buildId, ping.environment.build.buildId);
   // Test that we have the correct clientId.
   Assert.equal(ping.clientId, gClientID, "The correct clientId must be reported.");
 });
 
 add_task(function* test_archivePings() {
-  const ARCHIVE_PATH =
-    OS.Path.join(OS.Constants.Path.profileDir, "datareporting", "archived");
-
   let now = new Date(2009, 10, 18, 12, 0, 0);
   fakeNow(now);
 
   // Disable ping upload so that pings don't get sent.
   // With unified telemetry the FHR upload pref controls this,
   // with non-unified telemetry the Telemetry enabled pref.
   const isUnified = Preferences.get(PREF_UNIFIED, false);
   const uploadPref = isUnified ? PREF_FHR_UPLOAD_ENABLED : PREF_ENABLED;

--- a/toolkit/components/telemetry/tests/unit/test_TelemetryEnvironment.js
+++ b/toolkit/components/telemetry/tests/unit/test_TelemetryEnvironment.js
@@ -939,17 +939,16 @@ add_task(function* test_prefWatch_prefRe
 });
 
 add_task(function* test_addonsWatch_InterestingChange() {
   const ADDON_INSTALL_URL = gDataRoot + "restartless.xpi";
   const ADDON_ID = "tel-restartless-xpi@tests.mozilla.org";
   // We only expect a single notification for each install, uninstall, enable, disable.
   const EXPECTED_NOTIFICATIONS = 4;
 
-  let deferred = PromiseUtils.defer();
   let receivedNotifications = 0;
 
   let registerCheckpointPromise = (aExpected) => {
     return new Promise(resolve => TelemetryEnvironment.registerChangeListener(
       "testWatchAddons_Changes" + aExpected, (reason, data) => {
         Assert.equal(reason, "addons-changed");
         receivedNotifications++;
         resolve();
@@ -1261,17 +1260,16 @@ add_task(function* test_collectionWithbr
     foreignInstall: false,
     hasBinaryComponents: false,
     installDay: ADDON_INSTALL_DATE,
     updateDay: ADDON_INSTALL_DATE,
     signedState: mozinfo.addon_signing ? AddonManager.SIGNEDSTATE_MISSING :
                                          AddonManager.SIGNEDSTATE_NOT_REQUIRED,
   };
 
-  let deferred = PromiseUtils.defer();
   let receivedNotifications = 0;
 
   let registerCheckpointPromise = (aExpected) => {
     return new Promise(resolve => TelemetryEnvironment.registerChangeListener(
       "testBrokenAddon_collection" + aExpected, (reason, data) => {
         Assert.equal(reason, "addons-changed");
         receivedNotifications++;
         resolve();

--- a/toolkit/components/telemetry/tests/unit/test_TelemetryReportingPolicy.js
+++ b/toolkit/components/telemetry/tests/unit/test_TelemetryReportingPolicy.js
@@ -187,17 +187,17 @@ add_task(function* test_userNotifiedOfCu
 
   // Forcing a policy version should not automatically make the user notified.
   Preferences.set(PREF_ACCEPTED_POLICY_VERSION,
                   TelemetryReportingPolicy.DEFAULT_DATAREPORTING_POLICY_VERSION);
   Assert.ok(!TelemetryReportingPolicy.testIsUserNotified(),
                  "The default state of the date should have a time of 0 and it should therefore fail");
 
   // Showing the notification bar should make the user notified.
-  let now = fakeNow(2012, 11, 11);
+  fakeNow(2012, 11, 11);
   TelemetryReportingPolicy.testInfobarShown();
   Assert.ok(TelemetryReportingPolicy.testIsUserNotified(),
             "Using the proper API causes user notification to report as true.");
 
   // It is assumed that later versions of the policy will incorporate previous
   // ones, therefore this should also return true.
   let newVersion =
     Preferences.get(PREF_CURRENT_POLICY_VERSION, 1) + 1;

--- a/toolkit/components/telemetry/tests/unit/test_TelemetrySend.js
+++ b/toolkit/components/telemetry/tests/unit/test_TelemetrySend.js
@@ -172,17 +172,17 @@ add_task(function* test_sendPendingPings
 
   Assert.equal(countByType.get(TEST_TYPE_A), 5, "Should have received the correct amount of type A pings");
 
   yield TelemetrySend.testWaitOnOutgoingPings();
   PingServer.resetPingHandler();
 });
 
 add_task(function* test_sendDateHeader() {
-  let now = fakeNow(new Date(Date.UTC(2011, 1, 1, 11, 0, 0)));
+  fakeNow(new Date(Date.UTC(2011, 1, 1, 11, 0, 0)));
   yield TelemetrySend.reset();
 
   let pingId = yield TelemetryController.submitExternalPing("test-send-date-header", {});
   let req = yield PingServer.promiseNextRequest();
   let ping = decodeRequestPayload(req);
   Assert.equal(req.getHeader("Date"), "Tue, 01 Feb 2011 11:00:00 GMT",
                "Telemetry should send the correct Date header with requests.");
   Assert.equal(ping.id, pingId, "Should have received the correct ping id.");

--- a/toolkit/components/telemetry/tests/unit/test_TelemetrySendOldPings.js
+++ b/toolkit/components/telemetry/tests/unit/test_TelemetrySendOldPings.js
@@ -173,17 +173,17 @@ add_task(function* setupEnvironment() {
   yield TelemetryStorage.testClearPendingPings();
 });
 
 /**
  * Test that really recent pings are sent on Telemetry initialization.
  */
 add_task(function* test_recent_pings_sent() {
   let pingTypes = [{ num: RECENT_PINGS }];
-  let recentPings = yield createSavedPings(pingTypes);
+  yield createSavedPings(pingTypes);
 
   yield TelemetryController.testReset();
   yield TelemetrySend.testWaitOnOutgoingPings();
   assertReceivedPings(RECENT_PINGS);
 
   yield TelemetryStorage.testClearPendingPings();
 });
 

--- a/toolkit/components/telemetry/tests/unit/test_TelemetrySession.js
+++ b/toolkit/components/telemetry/tests/unit/test_TelemetrySession.js
@@ -1099,19 +1099,16 @@ add_task(function* test_dailyOverdue() {
 });
 
 add_task(function* test_environmentChange() {
   if (gIsAndroid) {
     // We don't split subsessions on environment changes yet on Android.
     return;
   }
 
-  let timerCallback = null;
-  let timerDelay = null;
-
   yield TelemetryStorage.testClearPendingPings();
   PingServer.clearRequests();
 
   let now = fakeNow(2040, 1, 1, 12, 0, 0);
   gMonotonicNow = fakeMonotonicNow(gMonotonicNow + 10 * MILLISECONDS_PER_MINUTE);
 
   const PREF_TEST = "toolkit.telemetry.test.pref1";
   Preferences.reset(PREF_TEST);
@@ -1240,18 +1237,18 @@ add_task(function* test_savedSessionData
   // Start TelemetrySession so that it loads the session data file.
   yield TelemetryController.testReset();
   Assert.equal(0, getSnapshot("TELEMETRY_SESSIONDATA_FAILED_LOAD").sum);
   Assert.equal(0, getSnapshot("TELEMETRY_SESSIONDATA_FAILED_PARSE").sum);
   Assert.equal(0, getSnapshot("TELEMETRY_SESSIONDATA_FAILED_VALIDATION").sum);
 
   // Watch a test preference, trigger and environment change and wait for it to propagate.
   // _watchPreferences triggers a subsession notification
-  let now = fakeNow(new Date(2050, 1, 1, 12, 0, 0));
   gMonotonicNow = fakeMonotonicNow(gMonotonicNow + 10 * MILLISECONDS_PER_MINUTE);
+  fakeNow(new Date(2050, 1, 1, 12, 0, 0));
   TelemetryEnvironment.testWatchPreferences(PREFS_TO_WATCH);
   let changePromise = new Promise(resolve =>
     TelemetryEnvironment.registerChangeListener("test_fake_change", resolve));
   Preferences.set(PREF_TEST, 1);
   yield changePromise;
   TelemetryEnvironment.unregisterChangeListener("test_fake_change");
 
   let payload = TelemetrySession.getPayload();
@@ -1463,17 +1460,17 @@ add_task(function* test_abortedSession_S
   // Fake scheduler functions to control aborted-session flow in tests.
   fakeSchedulerTimer(callback => schedulerTickCallback = callback, () => {});
   yield TelemetryController.testReset();
 
   Assert.ok((yield OS.File.exists(DATAREPORTING_PATH)),
             "Telemetry must create the aborted session directory when starting.");
 
   // Fake now again so that the scheduled aborted-session save takes place.
-  now = fakeNow(futureDate(now, ABORTED_SESSION_UPDATE_INTERVAL_MS));
+  fakeNow(futureDate(now, ABORTED_SESSION_UPDATE_INTERVAL_MS));
   // The first aborted session checkpoint must take place right after the initialisation.
   Assert.ok(!!schedulerTickCallback);
   // Execute one scheduler tick.
   yield schedulerTickCallback();
   // Check that the aborted session is due at the correct time.
   Assert.ok((yield OS.File.exists(ABORTED_FILE)), "There must be an aborted session ping.");
 
   // Remove the aborted session file and then shut down to make sure exceptions (e.g file
@@ -1614,17 +1611,17 @@ add_task(function* test_schedulerEnviron
   let nowDate = fakeNow(2060, 10, 18, 0, 0, 0);
   gMonotonicNow = fakeMonotonicNow(gMonotonicNow + 10 * MILLISECONDS_PER_MINUTE);
   let schedulerTickCallback = null;
   fakeSchedulerTimer(callback => schedulerTickCallback = callback, () => {});
   yield TelemetryController.testReset();
   TelemetryEnvironment.testWatchPreferences(PREFS_TO_WATCH);
 
   // Set the current time at midnight.
-  let future = fakeNow(futureDate(nowDate, MS_IN_ONE_DAY));
+  fakeNow(futureDate(nowDate, MS_IN_ONE_DAY));
   gMonotonicNow = fakeMonotonicNow(gMonotonicNow + 10 * MILLISECONDS_PER_MINUTE);
 
   // Trigger the environment change.
   Preferences.set(PREF_TEST, 1);
 
   // Wait for the environment-changed ping.
   yield PingServer.promiseNextPing();
 
@@ -1901,17 +1898,17 @@ add_task(function* test_changeThrottling
   // Set the Environment preferences to watch.
   TelemetryEnvironment.testWatchPreferences(PREFS_TO_WATCH);
 
   // The first pref change should not trigger a notification.
   Preferences.set(PREF_TEST, 1);
   Assert.equal(getSubsessionCount(), 1);
 
   // We should get a change notification after the 5min throttling interval.
-  now = fakeNow(futureDate(now, 5 * MILLISECONDS_PER_MINUTE + 1));
+  fakeNow(futureDate(now, 5 * MILLISECONDS_PER_MINUTE + 1));
   gMonotonicNow = fakeMonotonicNow(gMonotonicNow + 5 * MILLISECONDS_PER_MINUTE + 1);
   Preferences.set(PREF_TEST, 2);
   Assert.equal(getSubsessionCount(), 2);
 
   // After that, changes should be throttled again.
   now = fakeNow(futureDate(now, 1 * MILLISECONDS_PER_MINUTE));
   gMonotonicNow = fakeMonotonicNow(gMonotonicNow + 1 * MILLISECONDS_PER_MINUTE);
   Preferences.set(PREF_TEST, 3);

--- a/toolkit/components/telemetry/tests/unit/test_nsITelemetry.js
+++ b/toolkit/components/telemetry/tests/unit/test_nsITelemetry.js
@@ -140,20 +140,18 @@ add_task(function* test_noSerialization(
   do_check_false("NEWTAB_PAGE_PINNED_SITES_COUNT" in Telemetry.histogramSnapshots);
 });
 
 add_task(function* test_boolean_histogram() {
   var h = Telemetry.getHistogramById("TELEMETRY_TEST_BOOLEAN");
   var r = h.snapshot().ranges;
   // boolean histograms ignore numeric parameters
   do_check_eq(uneval(r), uneval([0, 1, 2]))
-  var sum = 0
   for (var i=0;i<r.length;i++) {
     var v = r[i];
-    sum += v;
     h.add(v);
   }
   h.add(true);
   h.add(false);
   var s = h.snapshot();
   do_check_eq(s.histogram_type, Telemetry.HISTOGRAM_BOOLEAN);
   // last bucket should always be 0 since .add parameters are normalized to either 0 or 1
   do_check_eq(s.counts[2], 0);

--- a/toolkit/components/thumbnails/PageThumbs.jsm
+++ b/toolkit/components/thumbnails/PageThumbs.jsm
@@ -847,17 +847,16 @@ var PageThumbsExpiration = {
       if (typeof filter == "function")
         filter(filterCallback)
       else
         filter.filterForThumbnailExpiration(filterCallback);
     }
   },
 
   expireThumbnails: function Expiration_expireThumbnails(aURLsToKeep) {
-    let path = this.path;
     let keep = aURLsToKeep.map(url => PageThumbsStorage.getLeafNameForURL(url));
     let msg = [
       PageThumbsStorage.path,
       keep,
       EXPIRATION_MIN_CHUNK_SIZE
     ];
 
     return PageThumbsWorker.post(

--- a/toolkit/components/thumbnails/test/browser_thumbnails_storage_migrate3.js
+++ b/toolkit/components/thumbnails/test/browser_thumbnails_storage_migrate3.js
@@ -17,24 +17,20 @@ XPCOMUtils.defineLazyServiceGetter(this,
   "@mozilla.org/file/directory_service;1", "nsIProperties");
 
 /**
  * This test makes sure we correctly migrate to thumbnail storage version 3.
  * This means copying existing thumbnails from the roaming to the local profile
  * directory and should just apply to Linux.
  */
 function* runTests() {
-  let dirSvc = Cc["@mozilla.org/file/directory_service;1"]
-                 .getService(Ci.nsIProperties);
-
   // Prepare a local profile directory.
   let localProfile = FileUtils.getDir("ProfD", ["local-test"], true);
   changeLocation("ProfLD", localProfile);
 
-  let local = FileUtils.getDir("ProfLD", [THUMBNAIL_DIRECTORY], true);
   let roaming = FileUtils.getDir("ProfD", [THUMBNAIL_DIRECTORY], true);
 
   // Set up some data in the roaming profile.
   let name = PageThumbsStorage.getLeafNameForURL(URL);
   let file = FileUtils.getFile("ProfD", [THUMBNAIL_DIRECTORY, name]);
   writeDummyFile(file);
 
   name = PageThumbsStorage.getLeafNameForURL(URL2);

--- a/toolkit/components/tooltiptext/tests/browser_bug581947.js
+++ b/toolkit/components/tooltiptext/tests/browser_bug581947.js
@@ -1,11 +1,10 @@
 function check(aBrowser, aElementName, aBarred, aType) {
   return ContentTask.spawn(aBrowser, [aElementName, aBarred, aType], function*([aElementName, aBarred, aType]) {
-    let doc = content.document;
     let e = content.document.createElement(aElementName);
     let contentElement = content.document.getElementById('content');
     contentElement.appendChild(e);
 
     if (aType) {
       e.type = aType;
     }
 
@@ -34,17 +33,16 @@ function check(aBrowser, aElementName, a
     contentElement.removeAttribute('novalidate');
 
     e.remove();
   });
 }
 
 function todo_check(aBrowser, aElementName, aBarred) {
   return ContentTask.spawn(aBrowser, [aElementName, aBarred], function*([aElementName, aBarred]) {
-    let doc = content.document;
     let e = content.document.createElement(aElementName);
     let contentElement = content.document.getElementById('content');
     contentElement.appendChild(e);
 
     let caught = false;
     try {
       e.setCustomValidity('foo');
     } catch (e) {
@@ -82,9 +80,8 @@ add_task(function*() {
       [ 'keygen', 'false' ],
     ];
 
     for (let data of todo_testData) {
       yield todo_check(browser, data[0], data[1]);
     }
   });
 });
-

--- a/toolkit/components/viewsource/content/viewSource-content.js
+++ b/toolkit/components/viewsource/content/viewSource-content.js
@@ -232,18 +232,18 @@ var ViewSourceContent = {
                                     .currentDescriptor;
       } catch (e) {
         // We couldn't get the page descriptor, so we'll probably end up re-retrieving
         // this document off of the network.
       }
 
       let utils = requestor.getInterface(Ci.nsIDOMWindowUtils);
       let doc = contentWindow.document;
-      let forcedCharSet = utils.docCharsetIsForced ? doc.characterSet
-                                                   : null;
+      forcedCharSet = utils.docCharsetIsForced ? doc.characterSet
+                                               : null;
     }
 
     this.loadSource(URL, pageDescriptor, lineNumber, forcedCharSet);
   },
 
   /**
    * Called when the parent is using the deprecated API for viewSource.xul.
    * This function will throw if it's called on a remote browser.
@@ -284,17 +284,16 @@ var ViewSourceContent = {
    * @param lineNumber (optional)
    *        The line number to focus as soon as the source has finished
    *        loading.
    * @param forcedCharSet (optional)
    *        The document character set to use instead of the default one.
    */
   loadSource(URL, pageDescriptor, lineNumber, forcedCharSet) {
     const viewSrcURL = "view-source:" + URL;
-    let loadFromURL = false;
 
     if (forcedCharSet) {
       docShell.charset = forcedCharSet;
     }
 
     if (lineNumber && lineNumber > 0) {
       let doneLoading = (event) => {
         // Ignore possible initial load of about:blank

--- a/toolkit/components/viewsource/content/viewSourceUtils.js
+++ b/toolkit/components/viewsource/content/viewSourceUtils.js
@@ -122,17 +122,16 @@ var gViewSourceUtils = {
 
       let browserToOpenIn = aGetBrowserFn ? aGetBrowserFn() : null;
       if (browserToOpenIn) {
         let viewSourceBrowser = new ViewSourceBrowser(browserToOpenIn);
         viewSourceBrowser.loadViewSourceFromSelection(message.data.uri, message.data.drawSelection,
                                                       message.data.baseURI);
       }
       else {
-        let docUrl = null;
         window.openDialog("chrome://global/content/viewPartialSource.xul",
                           "_blank", "all,dialog=no",
                           {
                             URI: message.data.uri,
                             drawSelection: message.data.drawSelection,
                             baseURI: message.data.baseURI,
                             partial: true,
                           });

--- a/toolkit/components/viewsource/test/browser/browser_gotoline.js
+++ b/toolkit/components/viewsource/test/browser/browser_gotoline.js
@@ -14,17 +14,16 @@ add_task(function*() {
 
   win = yield loadViewSourceWindow("data:text/plain," + encodeURIComponent(content));
   yield checkViewSource(win);
   yield BrowserTestUtils.closeWindow(win);
 });
 
 var checkViewSource = Task.async(function* (aWindow) {
   is(aWindow.gBrowser.contentDocument.body.textContent, content, "Correct content loaded");
-  let selection = aWindow.gBrowser.contentWindow.getSelection();
   let statusPanel = aWindow.document.getElementById("statusbar-line-col");
   is(statusPanel.getAttribute("label"), "", "Correct status bar text");
 
   for (let i = 1; i <= 3; i++) {
     aWindow.viewSourceChrome.goToLine(i);
     yield ContentTask.spawn(aWindow.gBrowser, i, function*(i) {
       let selection = content.getSelection();
       Assert.equal(selection.toString(), "line " + i, "Correct text selected");

--- a/toolkit/components/workerloader/require.js
+++ b/toolkit/components/workerloader/require.js
@@ -116,18 +116,16 @@
 
       // Make module available immediately
       // (necessary in case of circular dependencies)
       if (modules.has(path)) {
         return modules.get(path).exports;
       }
       modules.set(path, module);
 
-      let name = ":" + path;
-      let objectURL;
       try {
         // Load source of module, synchronously
         let xhr = new XMLHttpRequest();
         xhr.open("GET", uri, false);
         xhr.responseType = "text";
         xhr.send();