I must have been fast asleep when I reported the bug, because X does not crash at all.
The problem is that the screen goes blank (black). If I then blindly press the right buttons I can still exit X. Sometimes VGA mode displays correctly and it is possible to restart X (I do not use XDM). In other cases the screen remains black when X has shut down and my only option is to login from another host and initiate the dreaded shutdown -r The problem is not the application, because I can run mozilla without problems with the DISPLAY on another server (host) without problems. The symptoms seem consistent and repeatable. /g
