I'm trying to make a Firefox extension but have no idea how to do it.

It's extremely simple (pseudo code):
if IPaddress == "":
pref.cache = false
No preferences, UI or anything. Just that for development use. So as
soon as it's installed, its always active for the localhost IP.

I've been looking around for a few hours but I'm sure someone can
solve it for me in a few seconds :P