Use XMLHttpRequest constructor in JS modules

lib/downloader.js

 /*
  * This file is part of Adblock Plus <http://adblockplus.org/>,
  * Copyright (C) 2006-2013 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 230 matching lines @@
             this._download(downloadable, redirects + 1);
           }.bind(this);
         }
 
         this.onDownloadError(downloadable, downloadURL, error, channelStatus, responseStatus, redirectCallback);
       }
     }.bind(this);
 
     try
     {
-      request = Cc["@mozilla.org/xmlextras/xmlhttprequest;1"].createInstance(Ci.nsIXMLHttpRequest);
+      request = new XMLHttpRequest();
       request.mozBackgroundRequest = true;
       request.open("GET", downloadURL);
     }
     catch (e)
     {
       errorCallback("synchronize_invalid_url");
       return;
     }
 
     try {
@@ skipping 114 matching lines @@
    * @type Integer
    */
   softExpiration: 0,
 
   /**
    * Hard expiration interval, this is fixed.
    * @type Integer
    */
   hardExpiration: 0,
 };