Fennec, a.k.a. Firefox Mobile, is making great strides. The team released their second alpha today and it's a huge improvement over Alpha 1.
I've been playing with Fennec nighly builds on an n810 for a couple of weeks now and it's really starting to get usable. If you've got a device that can run it, I encourage you to give it a try and report any bugs to the Fennec team.