FF3 is faster, from atleast FF2, that's what I have seen in my short time with FF3. But then Opera was already faster than FF2 so I don't see any major difference between Opera 9.5 and Firefox. Even I have found some incompatibility issues with some addons in firefox but I hope they are ironed out soon.
I'll use both Opera and Firefox for now. Both are cool but I would really like a Speed-dial like addon for Firefox.