according to this article Firefox is the next update to Firebird so if you're using firebird I don't think you'll see much difference.

However I am about to d/l and try firefox so I might be able to give you a more informed response in a little while

Z

[EDIT]
ok, after using it for a couple of hours tonight... it's almost exactly the same as firebird... a couple of enhancements but really nothing that would make you want to not use it - up to you if you want to try it though.
[/EDIT]