Hook DOM APIs

Hi everyone,

I am a newbie in this area. I am thinking about a way to monitor an
arbitrary DOM object access. For example, if document.cookie has been
monitored, a notification will be generated whenever a javascript code
is trying to access the cookie.

Does this require modification of the firefox browser source code? If
not, what are the easier ways to do it? If it does, could anyone give
me some advices on how to make the right code changes at the right
places?

Thanks a lot!
Canny