Only with libthtread_xu,
when opening dialogue boxes for choosing files,
like when you choose "Save As",
FireFox 3  (wip/firefox) always crashes with the following error:

GThread-ERROR **: file gthread-posix.c: line 348
(g_thread_create_posix_impl): error 'Operation not supported' during
'pthread_attr_setschedparam (&attr, &sched)'