Added the dbg packages for what I could, and printed a bt for all threads while it was spinning. Hopefully this will help a little.

Let me know what else is useful information. I seem to be able to reproduce this easily now. :)

Thread 7 (Thread 0x424f6950 (LWP 8539)):
#0  0x00007f55df447aa6 in poll () from /lib/libc.so.6
#1  0x00007f55d6c4c450 in PR_Poll (pds=0x7795c8, npds=1, timeout=4294967295) at ptio.c:3895
#2  0x00007f55d5cbb120 in ?? () from /usr/lib/xulrunner-1.9b3/libxul.so
#3  0x00007f55d5cbb5bb in ?? () from /usr/lib/xulrunner-1.9b3/libxul.so
#4  0x00007f55d5cbb7f9 in ?? () from /usr/lib/xulrunner-1.9b3/libxul.so
#5  0x00007f55d63b28ef in ?? () from /usr/lib/xulrunner-1.9b3/libxul.so
#6  0x00007f55d6387125 in ?? () from /usr/lib/xulrunner-1.9b3/libxul.so
#7  0x00007f55d5cbb3e0 in ?? () from /usr/lib/xulrunner-1.9b3/libxul.so
#8  0x00007f55d63b294d in ?? () from /usr/lib/xulrunner-1.9b3/libxul.so
#9  0x00007f55d6387125 in ?? () from /usr/lib/xulrunner-1.9b3/libxul.so
#10 0x00007f55d63b261b in ?? () from /usr/lib/xulrunner-1.9b3/libxul.so
#11 0x00007f55d6c501ca in _pt_root (arg=<value optimized out>) at ptthread.c:221
#12 0x00007f55df6e13f7 in start_thread () from /lib/libpthread.so.0
#13 0x00007f55df45095d in clone () from /lib/libc.so.6
#14 0x0000000000000000 in ?? ()

Thread 6 (Thread 0x419b2950 (LWP 8540)):
#0  0x00007f55df6e5e1d in pthread_cond_timedwait@@GLIBC_2.3.2 () from /lib/libpthread.so.0
#1  0x00007f55d6c49e29 in pt_TimedWait (cv=0x6cae08, ml=0x6cad50, timeout=673) at ptsynch.c:280
#2  0x00007f55d6c4aa5a in PR_WaitCondVar (cvar=0x6cae00, timeout=3673) at ptsynch.c:407
#3  0x00007f55d63b5134 in ?? () from /usr/lib/xulrunner-1.9b3/libxul.so
#4  0x00007f55d63b294d in ?? () from /usr/lib/xulrunner-1.9b3/libxul.so
#5  0x00007f55d6387125 in ?? () from /usr/lib/xulrunner-1.9b3/libxul.so
#6  0x00007f55d63b261b in ?? () from /usr/lib/xulrunner-1.9b3/libxul.so
#7  0x00007f55d6c501ca in _pt_root (arg=<value optimized out>) at ptthread.c:221
#8  0x00007f55df6e13f7 in start_thread () from /lib/libpthread.so.0
#9  0x00007f55df45095d in clone () from /lib/libc.so.6
#10 0x0000000000000000 in ?? ()

Thread 5 (Thread 0x42cf7950 (LWP 8541)):
#0  0x00007f55df6e5b99 in pthread_cond_wait@@GLIBC_2.3.2 () from /lib/libpthread.so.0
#1  0x00007f55d6c4aaec in PR_WaitCondVar (cvar=0xdc1f30, timeout=4294967295) at ptsynch.c:405
#2  0x00007f55d61cb34a in ?? () from /usr/lib/xulrunner-1.9b3/libxul.so
#3  0x00007f55d6c501ca in _pt_root (arg=<value optimized out>) at ptthread.c:221
#4  0x00007f55df6e13f7 in start_thread () from /lib/libpthread.so.0
#5  0x00007f55df45095d in clone () from /lib/libc.so.6
#6  0x0000000000000000 in ?? ()

Thread 4 (Thread 0x434f8950 (LWP 8542)):
#0  0x00007f55df6e5b99 in pthread_cond_wait@@GLIBC_2.3.2 () from /lib/libpthread.so.0
#1  0x00007f55d6c4aaec in PR_WaitCondVar (cvar=0xdc2370, timeout=4294967295) at ptsynch.c:405
#2  0x00007f55d61cc2ff in ?? () from /usr/lib/xulrunner-1.9b3/libxul.so
#3  0x00007f55d6c501ca in _pt_root (arg=<value optimized out>) at ptthread.c:221
#4  0x00007f55df6e13f7 in start_thread () from /lib/libpthread.so.0
#5  0x00007f55df45095d in clone () from /lib/libc.so.6
#6  0x0000000000000000 in ?? ()

Thread 3 (Thread 0x43cf9950 (LWP 8548)):
#0  0x00007f55df6e5e1d in pthread_cond_timedwait@@GLIBC_2.3.2 () from /lib/libpthread.so.0
---Type <return> to continue, or q <return> to quit---
#1  0x00007f55d6c49e29 in pt_TimedWait (cv=0xebad58, ml=0xec2fb8, timeout=0) at ptsynch.c:280
#2  0x00007f55d6c4aa5a in PR_WaitCondVar (cvar=0xebad50, timeout=60000) at ptsynch.c:407
#3  0x00007f55d6c4ab56 in PR_Wait (mon=0xec2fb0, timeout=1137676064) at ptsynch.c:584
#4  0x00007f55d5cf6740 in ?? () from /usr/lib/xulrunner-1.9b3/libxul.so
#5  0x00007f55d63b3e10 in ?? () from /usr/lib/xulrunner-1.9b3/libxul.so
#6  0x00007f55d63b294d in ?? () from /usr/lib/xulrunner-1.9b3/libxul.so
#7  0x00007f55d6387125 in ?? () from /usr/lib/xulrunner-1.9b3/libxul.so
#8  0x00007f55d63b261b in ?? () from /usr/lib/xulrunner-1.9b3/libxul.so
#9  0x00007f55d6c501ca in _pt_root (arg=<value optimized out>) at ptthread.c:221
#10 0x00007f55df6e13f7 in start_thread () from /lib/libpthread.so.0
#11 0x00007f55df45095d in clone () from /lib/libc.so.6
#12 0x0000000000000000 in ?? ()

Thread 2 (Thread 0x45cfd950 (LWP 8553)):
#0  0x00007f55df6e5b99 in pthread_cond_wait@@GLIBC_2.3.2 () from /lib/libpthread.so.0
#1  0x00007f55d6c4aaec in PR_WaitCondVar (cvar=0xe95010, timeout=4294967295) at ptsynch.c:405
#2  0x00007f55d6c4ab56 in PR_Wait (mon=0xefaca0, timeout=128) at ptsynch.c:584
#3  0x00007f55d5cf6740 in ?? () from /usr/lib/xulrunner-1.9b3/libxul.so
#4  0x00007f55d63b18ea in ?? () from /usr/lib/xulrunner-1.9b3/libxul.so
#5  0x00007f55d63b2923 in ?? () from /usr/lib/xulrunner-1.9b3/libxul.so
#6  0x00007f55d6387125 in ?? () from /usr/lib/xulrunner-1.9b3/libxul.so
#7  0x00007f55d63b261b in ?? () from /usr/lib/xulrunner-1.9b3/libxul.so
#8  0x00007f55d6c501ca in _pt_root (arg=<value optimized out>) at ptthread.c:221
#9  0x00007f55df6e13f7 in start_thread () from /lib/libpthread.so.0
#10 0x00007f55df45095d in clone () from /lib/libc.so.6
#11 0x0000000000000000 in ?? ()

Thread 1 (Thread 0x7f55e3429780 (LWP 8538)):
#0  0x00007f55d6382d89 in ?? () from /usr/lib/xulrunner-1.9b3/libxul.so
#1  0x00007f55d631bf33 in ?? () from /usr/lib/xulrunner-1.9b3/libxul.so
#2  0x00007f55d6333fca in ?? () from /usr/lib/xulrunner-1.9b3/libxul.so
#3  0x00007f55d6334eac in ?? () from /usr/lib/xulrunner-1.9b3/libxul.so
#4  0x00007f55d63b44a5 in ?? () from /usr/lib/xulrunner-1.9b3/libxul.so
#5  0x00007f55d63b4a05 in ?? () from /usr/lib/xulrunner-1.9b3/libxul.so
#6  0x00007f55d63b294d in ?? () from /usr/lib/xulrunner-1.9b3/libxul.so
#7  0x00007f55d63871f4 in ?? () from /usr/lib/xulrunner-1.9b3/libxul.so
#8  0x00007f55d6300057 in ?? () from /usr/lib/xulrunner-1.9b3/libxul.so
#9  0x00007f55d62eddfe in ?? () from /usr/lib/xulrunner-1.9b3/libxul.so
#10 0x00007f55e099a3b4 in g_main_context_dispatch () from /usr/lib/libglib-2.0.so.0
#11 0x00007f55e099d6c5 in ?? () from /usr/lib/libglib-2.0.so.0
#12 0x00007f55e099d9e5 in g_main_loop_run () from /usr/lib/libglib-2.0.so.0
#13 0x00007f55e2280d63 in IA__gtk_main () at /build/buildd/gtk+2.0-2.12.8/gtk/gtkmain.c:1163
#14 0x000000000041c120 in ?? ()
#15 0x00007f55df3971c4 in __libc_start_main () from /lib/libc.so.6
#16 0x000000000040dcb9 in ?? ()
#17 0x00007fffeb461e78 in ?? ()
#18 0x0000000000000000 in ?? ()



and again a few seconds later:



Thread 7 (Thread 0x424f6950 (LWP 8539)):
#0  0x00007f55df447aa6 in poll () from /lib/libc.so.6
#1  0x00007f55d6c4c450 in PR_Poll (pds=0x7795c8, npds=1, timeout=4294967295) at ptio.c:3895
#2  0x00007f55d5cbb120 in ?? () from /usr/lib/xulrunner-1.9b3/libxul.so
#3  0x00007f55d5cbb5bb in ?? () from /usr/lib/xulrunner-1.9b3/libxul.so
#4  0x00007f55d5cbb7f9 in ?? () from /usr/lib/xulrunner-1.9b3/libxul.so
#5  0x00007f55d63b28ef in ?? () from /usr/lib/xulrunner-1.9b3/libxul.so
#6  0x00007f55d6387125 in ?? () from /usr/lib/xulrunner-1.9b3/libxul.so
#7  0x00007f55d5cbb3e0 in ?? () from /usr/lib/xulrunner-1.9b3/libxul.so
#8  0x00007f55d63b294d in ?? () from /usr/lib/xulrunner-1.9b3/libxul.so
#9  0x00007f55d6387125 in ?? () from /usr/lib/xulrunner-1.9b3/libxul.so
#10 0x00007f55d63b261b in ?? () from /usr/lib/xulrunner-1.9b3/libxul.so
#11 0x00007f55d6c501ca in _pt_root (arg=<value optimized out>) at ptthread.c:221
#12 0x00007f55df6e13f7 in start_thread () from /lib/libpthread.so.0
#13 0x00007f55df45095d in clone () from /lib/libc.so.6
#14 0x0000000000000000 in ?? ()

Thread 6 (Thread 0x419b2950 (LWP 8540)):
#0  0x00007f55df6e5e1d in pthread_cond_timedwait@@GLIBC_2.3.2 () from /lib/libpthread.so.0
#1  0x00007f55d6c49e29 in pt_TimedWait (cv=0x6cae08, ml=0x6cad50, timeout=238) at ptsynch.c:280
#2  0x00007f55d6c4aa5a in PR_WaitCondVar (cvar=0x6cae00, timeout=1238) at ptsynch.c:407
#3  0x00007f55d63b5134 in ?? () from /usr/lib/xulrunner-1.9b3/libxul.so
#4  0x00007f55d63b294d in ?? () from /usr/lib/xulrunner-1.9b3/libxul.so
#5  0x00007f55d6387125 in ?? () from /usr/lib/xulrunner-1.9b3/libxul.so
#6  0x00007f55d63b261b in ?? () from /usr/lib/xulrunner-1.9b3/libxul.so
#7  0x00007f55d6c501ca in _pt_root (arg=<value optimized out>) at ptthread.c:221
#8  0x00007f55df6e13f7 in start_thread () from /lib/libpthread.so.0
#9  0x00007f55df45095d in clone () from /lib/libc.so.6
#10 0x0000000000000000 in ?? ()

Thread 5 (Thread 0x42cf7950 (LWP 8541)):
#0  0x00007f55df6e5b99 in pthread_cond_wait@@GLIBC_2.3.2 () from /lib/libpthread.so.0
#1  0x00007f55d6c4aaec in PR_WaitCondVar (cvar=0xdc1f30, timeout=4294967295) at ptsynch.c:405
#2  0x00007f55d61cb34a in ?? () from /usr/lib/xulrunner-1.9b3/libxul.so
#3  0x00007f55d6c501ca in _pt_root (arg=<value optimized out>) at ptthread.c:221
#4  0x00007f55df6e13f7 in start_thread () from /lib/libpthread.so.0
#5  0x00007f55df45095d in clone () from /lib/libc.so.6
#6  0x0000000000000000 in ?? ()

Thread 4 (Thread 0x434f8950 (LWP 8542)):
#0  0x00007f55df6e5b99 in pthread_cond_wait@@GLIBC_2.3.2 () from /lib/libpthread.so.0
#1  0x00007f55d6c4aaec in PR_WaitCondVar (cvar=0xdc2370, timeout=4294967295) at ptsynch.c:405
#2  0x00007f55d61cc2ff in ?? () from /usr/lib/xulrunner-1.9b3/libxul.so
#3  0x00007f55d6c501ca in _pt_root (arg=<value optimized out>) at ptthread.c:221
#4  0x00007f55df6e13f7 in start_thread () from /lib/libpthread.so.0
#5  0x00007f55df45095d in clone () from /lib/libc.so.6
#6  0x0000000000000000 in ?? ()

Thread 2 (Thread 0x45cfd950 (LWP 8553)):
#0  0x00007f55df6e5b99 in pthread_cond_wait@@GLIBC_2.3.2 () from /lib/libpthread.so.0
---Type <return> to continue, or q <return> to quit---
#1  0x00007f55d6c4aaec in PR_WaitCondVar (cvar=0xe95010, timeout=4294967295) at ptsynch.c:405
#2  0x00007f55d6c4ab56 in PR_Wait (mon=0xefaca0, timeout=128) at ptsynch.c:584
#3  0x00007f55d5cf6740 in ?? () from /usr/lib/xulrunner-1.9b3/libxul.so
#4  0x00007f55d63b18ea in ?? () from /usr/lib/xulrunner-1.9b3/libxul.so
#5  0x00007f55d63b2923 in ?? () from /usr/lib/xulrunner-1.9b3/libxul.so
#6  0x00007f55d6387125 in ?? () from /usr/lib/xulrunner-1.9b3/libxul.so
#7  0x00007f55d63b261b in ?? () from /usr/lib/xulrunner-1.9b3/libxul.so
#8  0x00007f55d6c501ca in _pt_root (arg=<value optimized out>) at ptthread.c:221
#9  0x00007f55df6e13f7 in start_thread () from /lib/libpthread.so.0
#10 0x00007f55df45095d in clone () from /lib/libc.so.6
#11 0x0000000000000000 in ?? ()

Thread 1 (Thread 0x7f55e3429780 (LWP 8538)):
#0  0x00007f55df6e5fe6 in pthread_cond_signal@@GLIBC_2.3.2 () from /lib/libpthread.so.0
#1  0x00007f55d6c4a968 in pt_PostNotifies (lock=<value optimized out>, unlock=133) at ptsynch.c:145
#2  0x00007f55d6c4ac3d in PR_Unlock (lock=0x6cad50) at ptsynch.c:236
#3  0x00007f55d63b4d2d in ?? () from /usr/lib/xulrunner-1.9b3/libxul.so
#4  0x00007f55d633420e in ?? () from /usr/lib/xulrunner-1.9b3/libxul.so
#5  0x00007f55d6334eac in ?? () from /usr/lib/xulrunner-1.9b3/libxul.so
#6  0x00007f55d63b44a5 in ?? () from /usr/lib/xulrunner-1.9b3/libxul.so
#7  0x00007f55d63b4a05 in ?? () from /usr/lib/xulrunner-1.9b3/libxul.so
#8  0x00007f55d63b294d in ?? () from /usr/lib/xulrunner-1.9b3/libxul.so
#9  0x00007f55d63871f4 in ?? () from /usr/lib/xulrunner-1.9b3/libxul.so
#10 0x00007f55d6300057 in ?? () from /usr/lib/xulrunner-1.9b3/libxul.so
#11 0x00007f55d62eddfe in ?? () from /usr/lib/xulrunner-1.9b3/libxul.so
#12 0x00007f55e099a3b4 in g_main_context_dispatch () from /usr/lib/libglib-2.0.so.0
#13 0x00007f55e099d6c5 in ?? () from /usr/lib/libglib-2.0.so.0
#14 0x00007f55e099d9e5 in g_main_loop_run () from /usr/lib/libglib-2.0.so.0
#15 0x00007f55e2280d63 in IA__gtk_main () at /build/buildd/gtk+2.0-2.12.8/gtk/gtkmain.c:1163
#16 0x000000000041c120 in ?? ()
#17 0x00007f55df3971c4 in __libc_start_main () from /lib/libc.so.6
#18 0x000000000040dcb9 in ?? ()
#19 0x00007fffeb461e78 in ?? ()
#20 0x0000000000000000 in ?? ()