Can we quit bitching for a second ?
I tried ff4 ß7 & 8 on linux. Both work as well or faster than ff3.6 on the same machine. WebGL is very impressive, but isn't enabled by default ; it's just a flip of a switch away, though (try the google chrome webgl demos, I really liked http://www.ninepointfive.org/ ).
I don't feel I've lost any function in the switch. It's stable, and fast considering the scope of this software. I've been using chrome, safari and IE recently too, and ff4 is at least on par with them when not outright better.
Extensions are a chance we'd be fool to object to.
All in all, thumb up, and I look forward for the final release.