How to capture a navigation event before it happens?

I hope this the right forum for this question.

I am trying to find all the urls in a given web page and since sometimes it
is possible that urls can be present in JavaScript or dynamically generated
by JS, I thought of following

[1] simulate a click on every dom element or nsIFrame and see if there is a 
navigation
event generate
[2] get the url from the navigation event.
[3] cancel the navigation event

I know it is possible to do this in IE and I have done this in past, don't
exactly remember the event or function name though. I would greatly
appreciate if the community can help me in this.

thanks in advance
cheers
harvinder