var httpRequestObserver =
{
  observe: function(subject, topic, data)
  {
      if(topic == "http-on-examine-response"){
                var httpChannel = subject.QueryInterface(Components.interfaces.nsIHttpChannel);
	    lastLocation=httpChannel.getResponseHeader("Location");
     }
  },

  get observerService() {
    return Components.classes["@mozilla.org/observer-service;1"]
                     .getService(Components.interfaces.nsIObserverService);
  },

  register: function()
  {
	 this.observerService.addObserver(this, http-on-examine-response", false);
  },

  unregister: function()
 {
	 this.observerService.removeObserver(this, "http-on-examine-response");
  }
};

httpRequestObserver.register();