Issue 5028 - Use browser namespace

lib/subscriptionInit.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 187 matching lines @@
 
   for (let subscription of subscriptions)
   {
     FilterStorage.addSubscription(subscription);
     if (subscription instanceof DownloadableSubscription &&
         !subscription.lastDownload)
       Synchronizer.execute(subscription);
   }
 
   if (firstRun && !Prefs.suppress_first_run_page)
-    browser.tabs.create({url: ext.getURL("firstRun.html")});
+    browser.tabs.create({url: browser.extension.getURL("firstRun.html")});
 
   initNotifications();
 }
 
 Promise.all([FilterNotifier.once("load"),
              Prefs.untilLoaded]).then(detectFirstRun)
                                 .then(getSubscriptions)
                                 .then(finishInitialization);
 
 /**
  * Indicates whether the default filter subscriptions have been added
  * again because there weren't any subscriptions even though this wasn't
  * the first run.
  *
  * @type {boolean}
  */
 exports.reinitialized = false;
 
 /**
  * Sets a callback that is called with an array of subscriptions to be added
  * during initialization. The callback must return an array of subscriptions
  * that will effectively be added.
  *
  * @param {function} callback
  */
 exports.setSubscriptionsCallback = callback =>
 {
   subscriptionsCallback = callback;
 };