It really depends what you compare it to. In itself, it's really quite a good little browser - after a quick check it seems to use less memory than its predecessor and starts up quicker too. Also looks sleeker.
Problem is, Chrome is quite frankly, well, better. It's faster, more responsive, more scalable and less of a resource hog... the only original issue with it was the lack of extension support. But chrome in my mind has well and truly caught up on that front. Firefox is a good browser in its own right, but unless it can hold par with Chrome it's not really going to get a huge amount of support...