--- a/addon-sdk/source/test/context-menu/test-helper.js
+++ b/addon-sdk/source/test/context-menu/test-helper.js
@@ -25,17 +25,17 @@ const TEST_DOC_URL = module.uri.replace(
 // This makes it easier to run tests by handling things like opening the menu,
 // opening new windows, making assertions, etc.  Methods on |test| can be called
 // on instances of this class.  Don't forget to call done() to end the test!
 // WARNING: This looks up items in popups by comparing labels, so don't give two
 // items the same label.
 function TestHelper(assert, done) {
   // Methods on the wrapped test can be called on this object.
   for (var prop in assert)
-    this[prop] = () => assert[prop].apply(assert, arguments);
+    this[prop] = (...args) => assert[prop].apply(assert, args);
   this.assert = assert;
   this.end = done;
   this.loaders = [];
   this.browserWindow = getMostRecentBrowserWindow();
   this.overflowThreshValue = require("sdk/preferences/service").
                              get(OVERFLOW_THRESH_PREF, OVERFLOW_THRESH_DEFAULT);
   this.done = this.done.bind(this);
 }

--- a/addon-sdk/source/test/event/helpers.js
+++ b/addon-sdk/source/test/event/helpers.js
@@ -21,17 +21,17 @@ const { defer } = require("sdk/core/prom
  *    A string representing the event type to waiting for.
  * @param {Boolean} [capture]
  *    If `true`, `capture` indicates that the user wishes to initiate capture.
  *
  * @returns {Promise}
  *    A promise resolved once the delay given is passed, or the object
  *    receives the event specified
  */
-const wait = (target, type, capture) => {
+const wait = function(target, type, capture) {
   let { promise, resolve, reject } = defer();
 
   if (!arguments.length) {
     setImmediate(resolve);
   }
   else if (typeof(target) === "number") {
     setTimeout(resolve, target);
   }
@@ -100,9 +100,9 @@ exports.ignoreNew = scenario(function(ou
 exports.FIFO = scenario(function(target, expected, actual) {
   on(target, "data", function($) actual.push($ + "#1"));
   on(target, "data", function($) actual.push($ + "#2"));
   on(target, "data", function($) actual.push($ + "#3"));
 
   return expected.reduce(function(result, value) {
     return result.concat(value + "#1", value + "#2", value + "#3");
   }, []);
-});
\ No newline at end of file
+});

--- a/browser/base/content/test/general/head.js
+++ b/browser/base/content/test/general/head.js
@@ -553,18 +553,18 @@ let FullZoomHelper = {
 
   BACK: 0,
   FORWARD: 1,
   navigate: function navigate(direction) {
     return new Promise(resolve => {
       let didPs = false;
       let didZoom = false;
 
-      gBrowser.addEventListener("pageshow", function (event) {
-        gBrowser.removeEventListener("pageshow", arguments.callee, true);
+      gBrowser.addEventListener("pageshow", function listener(event) {
+        gBrowser.removeEventListener("pageshow", listener, true);
         didPs = true;
         if (didZoom)
           resolve();
       }, true);
 
       if (direction == this.BACK)
         gBrowser.goBack();
       else if (direction == this.FORWARD)
@@ -713,19 +713,19 @@ function assertWebRTCIndicatorStatus(exp
     is(menu && !menu.hidden, !!expected, "WebRTC menu should be " + expectedState);
   }
 
   if (!("nsISystemStatusBar" in Ci)) {
     if (!expected) {
       let win = Services.wm.getMostRecentWindow("Browser:WebRTCGlobalIndicator");
       if (win) {
         yield new Promise((resolve, reject) => {
-          win.addEventListener("unload", (e) => {
+          win.addEventListener("unload", function listener(e) {
             if (e.target == win.document) {
-              win.removeEventListener("unload", arguments.callee);
+              win.removeEventListener("unload", listener);
               resolve();
             }
           }, false);
         });
       }
     }
     let indicator = Services.wm.getEnumerator("Browser:WebRTCGlobalIndicator");
     let hasWindow = indicator.hasMoreElements();

--- a/browser/components/places/tests/browser/browser_library_commands.js
+++ b/browser/components/places/tests/browser/browser_library_commands.js
@@ -55,17 +55,17 @@ add_task(function* test_date_container()
      "Copy command is enabled");
   ok(!PO._places.controller.isCommandEnabled("cmd_cut"),
      "Cut command is disabled");
   ok(PO._places.controller.isCommandEnabled("cmd_delete"),
      "Delete command is enabled");
 
   // Execute the delete command and check visit has been removed.
   let promiseURIRemoved = promiseHistoryNotification("onDeleteURI",
-                                                     () => TEST_URI.equals(arguments[0]));
+                                                     v => TEST_URI.equals(v));
   PO._places.controller.doCommand("cmd_delete");
   yield promiseURIRemoved;
 
   // Test live update of "History" query.
   is(historyNode.childCount, 0, "History node has no more children");
 
   historyNode.containerOpen = false;
 
@@ -120,17 +120,17 @@ add_task(function* test_query_on_toolbar
      "Copy command is enabled");
   ok(PO._places.controller.isCommandEnabled("cmd_cut"),
      "Cut command is enabled");
   ok(PO._places.controller.isCommandEnabled("cmd_delete"),
      "Delete command is enabled");
 
   // Execute the delete command and check bookmark has been removed.
   let promiseItemRemoved = promiseBookmarksNotification("onItemRemoved",
-                                                        () => query.guid == arguments[5]);
+                                                        (...args) => query.guid == args[5]);
   PO._places.controller.doCommand("cmd_delete");
   yield promiseItemRemoved;
 
   is((yield PlacesUtils.bookmarks.fetch(query.guid)), null,
      "Query node bookmark has been correctly removed");
 
   toolbarNode.containerOpen = false;
 

--- a/browser/components/places/tests/browser/head.js
+++ b/browser/components/places/tests/browser/head.js
@@ -165,23 +165,23 @@ function promiseBookmarksNotification(no
   info(`promiseBookmarksNotification: waiting for ${notification}`);
   return new Promise((resolve, reject) => {
     let proxifiedObserver = new Proxy({}, {
       get: (target, name) => {
         if (name == "QueryInterface")
           return XPCOMUtils.generateQI([ Ci.nsINavBookmarkObserver ]);
         info(`promiseBookmarksNotification: got ${name} notification`);
         if (name == notification)
-          return () => {
-            if (conditionFn.apply(this, arguments)) {
+          return (...args) => {
+            if (conditionFn.apply(this, args)) {
               clearTimeout(timeout);
               PlacesUtils.bookmarks.removeObserver(proxifiedObserver, false);
               executeSoon(resolve);
             } else {
-              info(`promiseBookmarksNotification: skip cause condition doesn't apply to ${JSON.stringify(arguments)}`);
+              info(`promiseBookmarksNotification: skip cause condition doesn't apply to ${JSON.stringify(args)}`);
             }
           }
         return () => {};
       }
     });
     PlacesUtils.bookmarks.addObserver(proxifiedObserver, false);
     let timeout = setTimeout(() => {
       PlacesUtils.bookmarks.removeObserver(proxifiedObserver, false);
@@ -193,18 +193,18 @@ function promiseBookmarksNotification(no
 function promiseHistoryNotification(notification, conditionFn) {
   info(`Waiting for ${notification}`);
   return new Promise((resolve, reject) => {
     let proxifiedObserver = new Proxy({}, {
       get: (target, name) => {
         if (name == "QueryInterface")
           return XPCOMUtils.generateQI([ Ci.nsINavHistoryObserver ]);
         if (name == notification)
-          return () => {
-            if (conditionFn.apply(this, arguments)) {
+          return (...args) => {
+            if (conditionFn.apply(this, args)) {
               clearTimeout(timeout);
               PlacesUtils.history.removeObserver(proxifiedObserver, false);
               executeSoon(resolve);
             }
           }
         return () => {};
       }
     });

--- a/toolkit/components/places/tests/bookmarks/test_bookmarks_notifications.js
+++ b/toolkit/components/places/tests/bookmarks/test_bookmarks_notifications.js
@@ -425,18 +425,18 @@ function expectNotifications() {
     get(target, name) {
       if (name == "check") {
         PlacesUtils.bookmarks.removeObserver(observer);
         return expectedNotifications =>
           Assert.deepEqual(notifications, expectedNotifications);
       }
 
       if (name.startsWith("onItem")) {
-        return () => {
-          let args = Array.from(arguments, arg => {
+        return (...origArgs) => {
+          let args = Array.from(origArgs, arg => {
             if (arg && arg instanceof Ci.nsIURI)
               return new URL(arg.spec);
             if (arg && typeof(arg) == "number" && arg >= Date.now() * 1000)
               return new Date(parseInt(arg/1000));
             return arg;
           });
           notifications.push({ name: name, arguments: args });
         }

--- a/toolkit/components/places/tests/bookmarks/test_keywords.js
+++ b/toolkit/components/places/tests/bookmarks/test_keywords.js
@@ -39,17 +39,17 @@ function expectNotifications() {
     get(target, name) {
       if (name == "check") {
         PlacesUtils.bookmarks.removeObserver(observer);
         return expectedNotifications =>
           Assert.deepEqual(notifications, expectedNotifications);
       }
 
       if (name.startsWith("onItemChanged")) {
-        return (id, prop, isAnno, val, lastMod, itemType, parentId, guid, parentGuid, oldVal) => {
+        return function(id, prop, isAnno, val, lastMod, itemType, parentId, guid, parentGuid, oldVal) {
           if (prop != "keyword")
             return;
           let args = Array.from(arguments, arg => {
             if (arg && arg instanceof Ci.nsIURI)
               return new URL(arg.spec);
             if (arg && typeof(arg) == "number" && arg >= Date.now() * 1000)
               return new Date(parseInt(arg/1000));
             return arg;

--- a/toolkit/components/places/tests/unit/test_keywords.js
+++ b/toolkit/components/places/tests/unit/test_keywords.js
@@ -51,17 +51,17 @@ function expectBookmarkNotifications() {
     get(target, name) {
       if (name == "check") {
         PlacesUtils.bookmarks.removeObserver(observer);
         return expectedNotifications =>
           Assert.deepEqual(notifications, expectedNotifications);
       }
 
       if (name.startsWith("onItemChanged")) {
-        return (itemId, property) => {
+        return function(itemId, property) {
           if (property != "keyword")
             return;
           let args = Array.from(arguments, arg => {
             if (arg && arg instanceof Ci.nsIURI)
               return new URL(arg.spec);
             if (arg && typeof(arg) == "number" && arg >= Date.now() * 1000)
               return new Date(parseInt(arg/1000));
             return arg;

--- a/toolkit/devtools/event-emitter.js
+++ b/toolkit/devtools/event-emitter.js
@@ -81,20 +81,20 @@ EventEmitter.prototype = {
    *        A promise which is resolved when the event next happens. The
    *        resolution value of the promise is the first event argument. If
    *        you need access to second or subsequent event arguments (it's rare
    *        that this is needed) then use aListener
    */
   once: function EventEmitter_once(aEvent, aListener) {
     let deferred = promise.defer();
 
-    let handler = (aEvent, aFirstArg) => {
+    let handler = (aEvent, aFirstArg, ...aRest) => {
       this.off(aEvent, handler);
       if (aListener) {
-        aListener.apply(null, arguments);
+        aListener.apply(null, [aEvent, aFirstArg, ...aRest]);
       }
       deferred.resolve(aFirstArg);
     };
 
     handler._originalListener = aListener;
     this.on(aEvent, handler);
 
     return deferred.promise;