NVIDIA proprietary driver is not buggy, for what we are doing (which is pure OpenGL). We are enabling hardware acceleration on X with the NVIDIA proprietary driver.
The FGLRX driver is crashier, it's blacklisted at the moment, this could change (everything hopefully will change :-) )
Yes, you can turn the whole driver blacklisting off by defining the MOZ_GLX_IGNORE_BLACKLIST environment variable. Just launch firefox with this command (you can use it in the properties of your desktop icon, too):
We did this blacklisting to put and end to the endless series of linux crashes that were caused by buggy graphics drivers, and were causing lots of grief among linux users ("firefox 4 is crashy!"). This was the top reason for crashiness on linux.
We are looking forward to un-blacklisting drivers as soon as they get good enough