Have you asked the Firefox people what API's they provide for custom add-on
development?
That's a good place to start.

Firefox is very hard to get started developing.  The documentation sucks.
After lots of fruitless searching, I found a great tutorial at
http://www.borngeek.com/firefox/toolbar-tutorial/  Essentially there is no
compilation, it is all XML and Javascript (or so I think).

Good luck.  I used to think IE development was bad until I found Firefox,
and I just don't get it's mindset.  I stay as far away from it as possible.

-- David