Created attachment 461203 [details] Stack trace On recent (as of late July 2010) trunk, I've seen relatively common browser hangs with #0 __lll_lock_wait () at ../nptl/sysdeps/unix/sysv/linux/x86_64/lowlevellock.S:136 #1 0x00007fa986ce160f in _L_lock_1172 () from /lib/libpthread.so.0 #2 0x00007fa986ce155a in __pthread_mutex_lock (mutex=0x7fa986fd5040) at pthread_mutex_lock.c:101 #3 0x0000000000407f53 in free () #4 0x00007fa98570d150 in nsProfileLock::Unlock() () from /home/hsivonen/Projects/obj-opt/dist/bin/libxul.so #5 0x00007fa98570d185 in nsProfileLock::RemovePidLockFiles() () on the top of the stack. This typically happens when closing a tab. However, I don't have proper steps to reproduce. Try opening http://www.whatwg.org/specs/web-apps/current-work/ in a tab, closing the tab and repeating until the browser hangs.
You crashed inside the malloc lock and then the signal handler tried to allocate memory.