How to add listener in firefox addon?

i've add on load event like

window.addEventListener("load", function() { myExtension.init(); }, false);

i want to know the the code the following two events:

• Before any pictures/flash/js are download
• When the page stops loading due to any reason (may be the user

  stopped it or any anyther reason)

Thank you for the help...

Use the DOMContentLoaded event.