I’ve been having weird segmentation faults with Quake Live lately as well, but they occur on both my Nvidia and ATI system. In my case I can’t even get to the server browser as it segfaults before then.
I’m using QLPrism, and have tried both 32bit and 64bit client. Haven’t got around to trying normal Firefox again though.
I’m probably having a different issue, though, as this occurs on 313 and I haven’t tested 319 yet.