Index: ext/common.js
===================================================================
new file mode 100644
--- /dev/null
+++ b/ext/common.js
@@ -0,0 +1,51 @@
+/*
+ * This file is part of Adblock Plus <http://adblockplus.org/>,
+ * Copyright (C) 2006-2014 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/>.
+ */
+
+
+(function()
+{
+  window.ext = {};
+
+  var EventTarget = ext._EventTarget = function(cancelable)
+  {
+    this._listeners = [];
+    this._cancelable = cancelable;
+  };
+  EventTarget.prototype = {
+    addListener: function(listener)
+    {
+      if (this._listeners.indexOf(listener) == -1)
+        this._listeners.push(listener);
+    },
+    removeListener: function(listener)
+    {
+      var idx = this._listeners.indexOf(listener);
+      if (idx != -1)
+        this._listeners.splice(idx, 1);
+    },
+    _dispatch: function(cancelable, args)
+    {
+      for (var i = 0; i < this._listeners.length; i++)
+      {
+        var result = this._listeners[i].apply(null, arguments);
+        if (this._cancelable && result === false)
+          return false;
+      }
+      return true;
+    }
+  };
+})();