Issue 5028 - Use browser namespace

ext/common.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
@@ skipping 31 matching lines @@
         results.push(listener(...args));
 
       return results;
     }
   };
 
 
   /* Message passing */
 
   ext.onMessage = new ext._EventTarget();
-
-
-  /* Background page */
-
-  ext.backgroundPage = {
-    sendMessage: browser.runtime.sendMessage
-  };
 }());