--- a/mobile/android/.eslintrc.js
+++ b/mobile/android/.eslintrc.js
@@ -12,28 +12,28 @@ module.exports = {
     "no-empty": "off",
     "no-native-reassign": "off",
     "no-nested-ternary": "off",
     "no-new-object": "off",
     "no-octal": "off",
     "no-redeclare": "off",
     "no-useless-call": "off",
     "no-useless-concat": "off",
-    "no-unused-vars": "off",
     "object-shorthand": "off",
   },
 
   "overrides": [{
     files: [
       // Bug 1425047.
       "chrome/**",
       // Bug 1425048.
       "components/extensions/**",
       // Bug 1425034.
       "modules/WebsiteMetadata.jsm",
       // Bug 1425051.
       "tests/browser/robocop/**",
     ],
     rules: {
+      "no-unused-vars": "off",
       "no-undef": "off",
     }
   }],
 };

--- a/mobile/android/components/ColorPicker.js
+++ b/mobile/android/components/ColorPicker.js
@@ -25,26 +25,26 @@ ColorPicker.prototype = {
 
   init: function(aParent, aTitle, aInitial) {
     this._domWin = aParent;
     this._initial = aInitial;
     this._title = aTitle;
   },
 
   open: function(aCallback) {
-    let p = new Prompt({
-                         window: this._domWin,
-                         title: this._title,
-                         buttons: [
-                           this.strings.GetStringFromName("inputWidgetHelper.set"),
-                           this.strings.GetStringFromName("inputWidgetHelper.cancel"),
-                         ],
-                       })
-                      .addColorPicker({ value: this._initial })
-                      .show((data) => {
+    new Prompt({
+      window: this._domWin,
+      title: this._title,
+      buttons: [
+        this.strings.GetStringFromName("inputWidgetHelper.set"),
+        this.strings.GetStringFromName("inputWidgetHelper.cancel"),
+      ],
+    })
+    .addColorPicker({ value: this._initial })
+    .show((data) => {
       if (data.button == 0)
         aCallback.done(data.color0);
       else
         aCallback.done(this._initial);
     });
   },
 
   classID: Components.ID("{430b987f-bb9f-46a3-99a5-241749220b29}"),

--- a/mobile/android/components/HelperAppDialog.js
+++ b/mobile/android/components/HelperAppDialog.js
@@ -146,17 +146,16 @@ HelperAppLauncherDialog.prototype = {
           aLauncher.cancel(Cr.NS_BINDING_ABORTED);
         }
       }.bind(this)).catch(Cu.reportError);
       return;
     }
 
     let bundle = Services.strings.createBundle("chrome://browser/locale/browser.properties");
 
-    let defaultHandler = new Object();
     let apps = HelperApps.getAppsForUri(aLauncher.source, {
       mimeType: aLauncher.MIMEInfo.MIMEType,
     });
 
     if (this._shouldAddSaveToDiskIntent(aLauncher)) {
       // Add a fake intent for save to disk at the top of the list.
       apps.unshift({
         name: bundle.GetStringFromName("helperapps.saveToDisk"),

--- a/mobile/android/components/LoginManagerPrompter.js
+++ b/mobile/android/components/LoginManagerPrompter.js
@@ -160,18 +160,16 @@ LoginManagerPrompter.prototype = {
    * save the specified login. This allows the user to see the results of
    * their login, and only save a login which they know worked.
    *
    */
   _showSaveLoginNotification: function(aLogin) {
     let brandShortName = this._strBundle.brand.GetStringFromName("brandShortName");
     let notificationText  = this._getLocalizedString("saveLogin", [brandShortName]);
 
-    let username = aLogin.username ? this._sanitizeUsername(aLogin.username) : "";
-
     // The callbacks in |buttons| have a closure to access the variables
     // in scope here; set one to |Services.logins| so we can get back to pwmgr
     // without a getService() call.
     var pwmgr = Services.logins;
     let promptHistogram = Services.telemetry.getHistogramById("PWMGR_PROMPT_REMEMBER_ACTION");
 
     var buttons = [
       {
@@ -263,18 +261,16 @@ LoginManagerPrompter.prototype = {
    *
    * Note: The caller doesn't know the username for aNewLogin, so this
    *       function fills in .username and .usernameField with the values
    *       from the login selected by the user.
    *
    * Note; XPCOM stupidity: |count| is just |logins.length|.
    */
   promptToChangePasswordWithUsernames: function(logins, count, aNewLogin) {
-    const buttonFlags = Ci.nsIPrompt.STD_YES_NO_BUTTONS;
-
     var usernames = logins.map(l => l.username);
     var dialogText  = this._getLocalizedString("userSelectText2");
     var dialogTitle = this._getLocalizedString("passwordChangeTitle");
     var selectedIndex = { value: null };
 
     // If user selects ok, outparam.value is set to the index
     // of the selected username.
     var ok = Services.prompt.select(null,

--- a/mobile/android/components/SessionStore.js
+++ b/mobile/android/components/SessionStore.js
@@ -177,17 +177,17 @@ SessionStore.prototype = {
       if (this._sessionFile.exists()) { this._sessionFile.remove(false); }
       if (this._sessionFileBackup.exists()) { this._sessionFileBackup.remove(false); }
       if (this._sessionFilePrevious.exists()) { this._sessionFilePrevious.remove(false); }
       if (this._sessionFileTemp.exists()) { this._sessionFileTemp.remove(false); }
     }
   },
 
   _forgetClosedTabs: function ss_forgetClosedTabs() {
-    for (let [ssid, win] of Object.entries(this._windows)) {
+    for (let win of Object.values(this._windows)) {
       win.closedTabs = [];
     }
 
     this._lastClosedTabIndex = INVALID_TAB_INDEX;
   },
 
   onEvent: function ss_onEvent(event, data, callback) {
     switch (event) {
@@ -1254,17 +1254,17 @@ SessionStore.prototype = {
       let selected = (i == aData.urls.length - 1);
       let params = {
         selected,
         delayLoad: !selected,
         isPrivate: false,
         desktopMode: false,
       };
 
-      let tab = window.BrowserApp.addTab(url, params);
+      window.BrowserApp.addTab(url, params);
     }
   },
 
   // This function iterates through a list of tab data restoring session for each of them.
   _restoreTabs: function ss_restoreTabs(aData) {
     let window = Services.wm.getMostRecentWindow("navigator:browser");
     for (let i = 0; i < aData.tabs.length; i++) {
       let tabData = JSON.parse(aData.tabs[i]);
@@ -1389,17 +1389,16 @@ SessionStore.prototype = {
       throw "Invalid session JSON: " + aData;
     }
 
     let window = Services.wm.getMostRecentWindow("navigator:browser");
     let tabs = state.windows[0].tabs;
 
     for (let i = 0; i < tabs.length; i++) {
       let tabData = tabs[i];
-      let entry = tabData.entries[tabData.index - 1];
 
       // Get the stubbed tab
       let tab = window.BrowserApp.getTabForId(tabData.tabId);
 
       // Don't restore tab if user has already closed it
       if (tab == null) {
         delete tabData.tabId;
         continue;

--- a/mobile/android/components/geckoview/GeckoViewPermission.js
+++ b/mobile/android/components/geckoview/GeckoViewPermission.js
@@ -177,17 +177,17 @@ GeckoViewPermission.prototype = {
     if (types.length !== 1) {
       aRequest.cancel();
       return;
     }
 
     let perm = types.queryElementAt(0, Ci.nsIContentPermissionType);
     let dispatcher = GeckoViewUtils.getDispatcherForWindow(
         aRequest.window ? aRequest.window : aRequest.element.ownerGlobal);
-    let promise = dispatcher.sendRequestForResult({
+    dispatcher.sendRequestForResult({
         type: "GeckoView:ContentPermission",
         uri: aRequest.principal.URI.displaySpec,
         perm: perm.type,
         access: perm.access !== "unused" ? perm.access : null,
     }).then(granted => {
       if (!granted) {
         return false;
       }

--- a/mobile/android/modules/DownloadNotifications.jsm
+++ b/mobile/android/modules/DownloadNotifications.jsm
@@ -14,18 +14,16 @@ ChromeUtils.defineModuleGetter(this, "No
 ChromeUtils.defineModuleGetter(this, "OS", "resource://gre/modules/osfile.jsm");
 ChromeUtils.defineModuleGetter(this, "Services", "resource://gre/modules/Services.jsm");
 ChromeUtils.defineModuleGetter(this, "Snackbars", "resource://gre/modules/Snackbars.jsm");
 ChromeUtils.defineModuleGetter(this, "UITelemetry", "resource://gre/modules/UITelemetry.jsm");
 
 XPCOMUtils.defineLazyServiceGetter(this, "ParentalControls",
   "@mozilla.org/parental-controls-service;1", "nsIParentalControlsService");
 
-var Log = ChromeUtils.import("resource://gre/modules/AndroidLog.jsm", {}).AndroidLog.i.bind(null, "DownloadNotifications");
-
 XPCOMUtils.defineLazyGetter(this, "strings",
                             () => Services.strings.createBundle("chrome://browser/locale/browser.properties"));
 
 Object.defineProperty(this, "window",
                       { get: () => Services.wm.getMostRecentWindow("navigator:browser") });
 
 const kButtons = {
   PAUSE: new DownloadNotificationButton("pause",

--- a/mobile/android/modules/InputWidgetHelper.jsm
+++ b/mobile/android/modules/InputWidgetHelper.jsm
@@ -35,17 +35,17 @@ var InputWidgetHelper = {
 
     this._uiBusy = true;
     this.show(aTarget);
     this._uiBusy = false;
   },
 
   show: function(aElement) {
     let type = aElement.getAttribute("type");
-    let p = new Prompt({
+    new Prompt({
       window: aElement.ownerGlobal,
       title: this.strings().GetStringFromName("inputWidgetHelper." + aElement.getAttribute("type")),
       buttons: [
         this.strings().GetStringFromName("inputWidgetHelper.set"),
         this.strings().GetStringFromName("inputWidgetHelper.clear"),
         this.strings().GetStringFromName("inputWidgetHelper.cancel")
       ],
     }).addDatePicker({

--- a/mobile/android/modules/MediaPlayerApp.jsm
+++ b/mobile/android/modules/MediaPlayerApp.jsm
@@ -4,17 +4,16 @@
  * You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 "use strict";
 
 this.EXPORTED_SYMBOLS = ["MediaPlayerApp"];
 
 ChromeUtils.import("resource://gre/modules/Services.jsm");
 ChromeUtils.import("resource://gre/modules/Messaging.jsm");
-var log = ChromeUtils.import("resource://gre/modules/AndroidLog.jsm", {}).AndroidLog.d.bind(null, "MediaPlayerApp");
 
 // Helper function for sending commands to Java.
 function send(type, data, callback) {
   let msg = {
     type: type
   };
 
   for (let i in data) {

--- a/mobile/android/modules/Prompt.jsm
+++ b/mobile/android/modules/Prompt.jsm
@@ -187,17 +187,16 @@ Prompt.prototype = {
     dispatcher.sendRequestForResult(this.msg).then((data) => {
       if (this.callback) {
         this.callback(data);
       }
     });
   },
 
   _setListItems: function(aItems) {
-    let hasSelected = false;
     this.msg.listitems = [];
 
     aItems.forEach(function(item) {
       let obj = { id: item.id };
 
       obj.label = item.label;
 
       if (item.disabled)

--- a/mobile/android/modules/Sanitizer.jsm
+++ b/mobile/android/modules/Sanitizer.jsm
@@ -13,20 +13,16 @@ XPCOMUtils.defineLazyModuleGetters(this,
   Downloads: "resource://gre/modules/Downloads.jsm",
   EventDispatcher: "resource://gre/modules/Messaging.jsm",
   FormHistory: "resource://gre/modules/FormHistory.jsm",
   OS: "resource://gre/modules/osfile.jsm",
   Task: "resource://gre/modules/Task.jsm",
   TelemetryStopwatch: "resource://gre/modules/TelemetryStopwatch.jsm",
 });
 
-function dump(a) {
-  Services.console.logStringMessage(a);
-}
-
 this.EXPORTED_SYMBOLS = ["Sanitizer"];
 
 function Sanitizer() {}
 Sanitizer.prototype = {
   clearItem: function(aItemName, startTime) {
     // Only a subset of items support deletion with startTime.
     // Those who do not will be rejected with error message.
     if (typeof startTime != "undefined") {

--- a/mobile/android/modules/geckoview/GeckoViewContentModule.jsm
+++ b/mobile/android/modules/geckoview/GeckoViewContentModule.jsm
@@ -10,19 +10,19 @@ ChromeUtils.import("resource://gre/modul
 
 ChromeUtils.defineModuleGetter(this, "EventDispatcher",
   "resource://gre/modules/Messaging.jsm");
 
 XPCOMUtils.defineLazyGetter(this, "dump", () =>
     ChromeUtils.import("resource://gre/modules/AndroidLog.jsm",
                        {}).AndroidLog.d.bind(null, "ViewContentModule"));
 
-function debug(aMsg) {
-  // dump(aMsg);
-}
+// function debug(aMsg) {
+//   dump(aMsg);
+// }
 
 class GeckoViewContentModule {
   constructor(aModuleName, aMessageManager) {
     this.moduleName = aModuleName;
     this.messageManager = aMessageManager;
     this.eventDispatcher = EventDispatcher.forMessageManager(aMessageManager);
 
     this.messageManager.addMessageListener(

--- a/mobile/android/modules/geckoview/GeckoViewModule.jsm
+++ b/mobile/android/modules/geckoview/GeckoViewModule.jsm
@@ -7,19 +7,19 @@
 this.EXPORTED_SYMBOLS = ["GeckoViewModule"];
 
 ChromeUtils.import("resource://gre/modules/XPCOMUtils.jsm");
 
 XPCOMUtils.defineLazyGetter(this, "dump", () =>
     ChromeUtils.import("resource://gre/modules/AndroidLog.jsm",
                        {}).AndroidLog.d.bind(null, "ViewModule"));
 
-function debug(aMsg) {
-  // dump(aMsg);
-}
+// function debug(aMsg) {
+//   dump(aMsg);
+// }
 
 class GeckoViewModule {
   constructor(aModuleName, aWindow, aBrowser, aEventDispatcher) {
     this.isRegistered = false;
     this.window = aWindow;
     this.browser = aBrowser;
     this.eventDispatcher = aEventDispatcher;
     this.moduleName = aModuleName;

--- a/mobile/android/modules/geckoview/GeckoViewTab.jsm
+++ b/mobile/android/modules/geckoview/GeckoViewTab.jsm
@@ -8,19 +8,19 @@ this.EXPORTED_SYMBOLS = ["GeckoViewTab"]
 
 ChromeUtils.import("resource://gre/modules/GeckoViewModule.jsm");
 ChromeUtils.import("resource://gre/modules/XPCOMUtils.jsm");
 
 XPCOMUtils.defineLazyGetter(this, "dump", () =>
     ChromeUtils.import("resource://gre/modules/AndroidLog.jsm",
                        {}).AndroidLog.d.bind(null, "ViewTab"));
 
-function debug(aMsg) {
-  // dump(aMsg);
-}
+// function debug(aMsg) {
+//   dump(aMsg);
+// }
 
 // Stub BrowserApp implementation for WebExtensions support.
 class GeckoViewTab extends GeckoViewModule {
   init() {
     this.browser.tab = { id: 0, browser: this.browser };
 
     this.window.gBrowser = this.window.BrowserApp = {
       selectedBrowser: this.browser,