help me with firefox addon

I need someone to help me with a firefox addon. I am trying to attach a listener event to a form on when a particular site is loaded. The listner must trigger when form is submitted. I have got the part on particular site loading, I only need your help attaching the listner. less than 20 minutes work. something like this? var f=I don't know what goes here [login to view URL]('form_id').addEventListner('onsubmit',function(){ [login to view URL]('form submitted'); }); You must know about firefox addons and must have created some. You must know about how to access the dom from the addon. You must know how to attach a listner event to a form that triggers onsubmit.