Yeah good point Saviour that would be using Google. I have looked at it a little when we were discussing a custom Computer Hope tool bar, but didn't play around with it probably enough. After downloading it I didn't really care for some of the features that I couldn't get removed.
Personally if I was going to go after this I'd just work on creating a custom toolbar from scratch since I think it'd be the only way I could get all the features I really wanted.
Unfortunately a lot of the Firefox toolbar relies on XML a language I'm afraid to admit is way low on my totem poll of knowledge.