--- a/testing/marionette/modal.js
+++ b/testing/marionette/modal.js
@@ -1,21 +1,21 @@
 /* This Source Code Form is subject to the terms of the Mozilla Public
  * License, v. 2.0. If a copy of the MPL was not distributed with this file,
  * You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 "use strict";
 
-var {utils: Cu} = Components;
+const {utils: Cu} = Components;
 
 Cu.import("resource://gre/modules/Services.jsm");
 
 this.EXPORTED_SYMBOLS = ["modal"];
 
-var isFirefox = () => Services.appinfo.name == "Firefox";
+const isFirefox = () => Services.appinfo.name == "Firefox";
 
 this.modal = {};
 modal = {
   COMMON_DIALOG_LOADED: "common-dialog-loaded",
   TABMODAL_DIALOG_LOADED: "tabmodal-dialog-loaded",
   handlers: {
     "common-dialog-loaded": new Set(),
     "tabmodal-dialog-loaded": new Set()