Monitor messages sent to an iframe

Steps to follow

1. Open Firebug, enable the Console and Script panels and reload.
2. Monitor "message" events sent to iframe on this page by executing this expression on the command line: monitorEvents($("iframe").contentWindow, "message")
3. You can modify a message send to the iframe:
   
4. Click this button to send the message to the iframe:
   Post Message
5. The Console panel should display an info about the message
6. You can cancel the monitoring by executing:
   unmonitorEvents($("iframe").contentWindow, "message")