It never was compatible with 3.0*?
* neglecting the fact that it's crap, doesn't really speed anything up, leaves all sorts of crap behind when you uninstall it etc
It did actually help the speed of mine due to us having the crapest of crap 480Kbps connections, it probably doesn't help speed things up on a 'modern' connection.
I'm pretty sure I've been using FasterFox since FF3 came out, maybe I used that toolkit that allows you to force compatibility, I can't remember.