gdb firefox with libthr -> fatal trap 9

I tried to run firefox from gdb and it caused a panic.  (The second time
I tried it, I started X then switched to a text VT to run "gdb
firefox-bin" so that the panic wouldn't cause an instant reboot)

I have libmap.conf set up so that firefox-bin uses libthr.  If I use
libpthread instead, there's no panic, firefox runs in the debugger.

Transcript of the panic follows:

kernel trap 9 with interrupts disabled


Fatal trap 9: general protection fault while in kernel mode
instruction pointer     = 0x20:0xc061558b
stack pointer           = 0x28:0xc7557cf0
frame pointer           = 0x28:0xc7557cf0
code segment            = base 0x0, limit 0xfffff, type 0x1b
                        = DPL 0, pres 1, def32 1, gran 1
processor eflags        = resume, IOPL = 0
current process         = 666 (firefox-bin)
[thread pid 666 tid 100082]
Stopped at      fpurstor+0xf:
db> where
Tracing pid 666 tid 100082 td 0xc13897d0
fpurstor(c7557dd0) at fpurstor+0xf
npxdna(0,0,0,3,c1388400) at npxdna+0xe5
trap(3b,3b,3b,8076c80,0) at trap+0x297
calltrap() at calltrap+0x5
--- trap 0x16, eip = 0x2885d02b, esp = 0xbfbfe520, ebp = 0xbfbfe538 ---
db> call doadump
Dumping 97 MB

Transcribed manually because doadump didn't.  =(  It just stopped,
although hitting keys caused it to print "[CTRL-C to abort]"

This is on 6-CURRENT from earlier today.  I'm not suggesting anything
has been broken recently since I've never tried to run firefox-bin from
gdb before.

--Emil (mildly amused by the process ID)