I don't know but FF is acting weird on my PC, I couldn't load FB on it most of the time, but Chrome can load it instantly, IMO, Chrome can run AJAX website better
Well, I don't see browsers actually needing to be 64-bit. In fact, I would be concerned if they "need" to be 64-bit. That would mean they need so much memory to run that 4 GB is just not enough.