Oct 13 spontaneous reboot

I had updated my source tree yesterday afternoon and everything worked.
Today's CURRENT spontaneously reboots every time I try to start firefox.

I have KDB in my kernel config and I can enter the debugger before I
start X11 with CTRL-ALT-ESC, but when firefox starts the next thing
that's visible on my screen is the BIOS startup.

I'll try narrowing down this to a specific time since yesterday noon, by
updating my sources to '2004/10/12 12:00:00 UTC' which was the last
version I know that worked and move in steps up to today's CURRENT, but
I just wanted to let everyone know that something seems very broken here.

- Giorgos