Comment 4 for bug 53569

I can confirm now that the crash happens not only when I close a window, but also when I close a tab in Firefox. This has happened to me at least twice. The system freezes (the mouse does move, but with delays) and the log files start growing very quickly. shift-alt-sysrq-k immediately logs me out and I can log in again without rebooting.

This bug is rather serious and I will probably have to install the 32-bit version of Ubuntu soon, as the AMD64 version is not very usable in this state.