Issue 5938 - Use top-level var for global variables

polyfill.js

 /*
  * This file is part of Adblock Plus <https://adblockplus.org/>,
  * Copyright (C) 2006-present eyeo GmbH
  *
  * Adblock Plus is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License version 3 as
  * published by the Free Software Foundation.
  *
  * Adblock Plus is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  * GNU General Public License for more details.
  *
  * You should have received a copy of the GNU General Public License
  * along with Adblock Plus.  If not, see <http://www.gnu.org/licenses/>.
  */
 
 "use strict";
 
+var browser;
+
 {
   const asyncAPIs = [
     "contextMenus.removeAll",
     "devtools.panels.create",
     "notifications.clear",
     "notifications.create",
     "runtime.openOptionsPage",
     "runtime.sendMessage",
     "runtime.setUninstallURL",
     "storage.local.get",
@@ skipping 95 matching lines @@
 
     return true;
   }
 
   if (shouldWrapAPIs())
   {
     // Unlike Firefox and Microsoft Edge, Chrome doesn't have a "browser" object,
     // but provides the extension API through the "chrome" namespace
     // (non-standard).
     if (typeof browser == "undefined")
-      window.browser = chrome;
+      browser = chrome;
 
     for (let api of asyncAPIs)
       wrapAPI(api);
   }
 
   // Workaround since HTMLCollection, NodeList, StyleSheetList, and CSSRuleList
   // didn't have iterator support before Chrome 51.
   // https://bugs.chromium.org/p/chromium/issues/detail?id=401699
   for (let object of [HTMLCollection, NodeList, StyleSheetList, CSSRuleList])
   {
     if (!(Symbol.iterator in object.prototype))
       object.prototype[Symbol.iterator] = Array.prototype[Symbol.iterator];
   }
 }