I finally upgraded to the latest KernelEx Beta a couple of days ago and got Firefox3.6 installed and looking how I wanted it, replacing my previous FireFox2.0.0.20 (I think - the last v2 anyway.) The next day, using it, I got graphics corruptions after a while, starting with the browser icons and then generally shifting to more snd more things including system icons, and getting thick black lines across webpages. The machine generally slowed down too. The only way of curing it was a complete reboot, but it would soon return. After much tearing of hair, I stumbled upon the idea of checking the graphics drivers and found a 2009 issue for my card (NVIDIA GeForce4 MX 420.) I was surprised, cos it's an older card, but this totally cured my problem. Everything is rock-solid now. It may not be the cause of your problem, though the symptoms seem to be the same, so worth checking.