Use XMLHttpRequest constructor in JS modules

lib/synchronizer.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 273 matching lines @@
 
         let fallbackURL = Prefs.subscriptions_fallbackurl;
         let {addonVersion} = require("info");
         fallbackURL = fallbackURL.replace(/%VERSION%/g, encodeURIComponent(addonVersion));
         fallbackURL = fallbackURL.replace(/%SUBSCRIPTION%/g, encodeURIComponent(subscription.url));
         fallbackURL = fallbackURL.replace(/%URL%/g, encodeURIComponent(downloadURL));
         fallbackURL = fallbackURL.replace(/%ERROR%/g, encodeURIComponent(error));
         fallbackURL = fallbackURL.replace(/%CHANNELSTATUS%/g, encodeURIComponent(channelStatus));
         fallbackURL = fallbackURL.replace(/%RESPONSESTATUS%/g, encodeURIComponent(responseStatus));
 
-        let request = Cc["@mozilla.org/xmlextras/xmlhttprequest;1"].createInstance(Ci.nsIXMLHttpRequest);
+        let request = new XMLHttpRequest();
         request.mozBackgroundRequest = true;
         request.open("GET", fallbackURL);
         request.overrideMimeType("text/plain");
         request.channel.loadFlags = request.channel.loadFlags |
                                     request.channel.INHIBIT_CACHING |
                                     request.channel.VALIDATE_ALWAYS;
         request.addEventListener("load", function(ev)
         {
           if (onShutdown.done)
             return;
 
           if (!(subscription.url in FilterStorage.knownSubscriptions))
             return;
 
           let match = /^(\d+)(?:\s+(\S+))?$/.exec(request.responseText);
           if (match && match[1] == "301" && match[2] && /^https?:\/\//i.test(match[2])) // Moved permanently
             redirectCallback(match[2]);
           else if (match && match[1] == "410")        // Gone
           {
             let data = "[Adblock]\n" + subscription.filters.map(function(f) f.text).join("\n");
             redirectCallback("data:text/plain," + encodeURIComponent(data));
           }
         }, false);
         request.send(null);
       }
     }
   },
 };
 Synchronizer.init();