Comment 6 for bug 583891

This also happens on Kubuntu, not using firefox. It can happen with different applications showing graphics, such as Akregator, Konqueror, etc. I found that you can actually predict when X is going to crash and bring you straight to login screen, because characters within the window start to be replaced by senseless symbols; or images within the frame of the window turn into thick coloured horizontal stripes. Whenever I see that, I immediately close the window in question, and go check the System log, which invariably shows such messages as:

2010-06-04 14:58:08 EGO kernel [20138.652499] [drm:radeon_cs_ioctl] *ERROR* Failed to parse relocation -12!
2010-06-04 14:58:08 EGO kernel [20139.291065] [drm:radeon_cs_ioctl] *ERROR* Failed to parse relocation -12!
2010-06-04 14:58:09 EGO kernel [20139.797174] [drm:radeon_cs_ioctl] *ERROR* Failed to parse relocation -12!

I found that this prevents crashes, and interruption to normal workflow. Still, it's merely a temporary workaround that doesn't solve the issue.