Xorg freezes in Build 125

I'm running Build 125 now for some days and now I recognized, for multiple times now, that Xorg is freezing. I'm using LCD and external Montior in dual screen mode.

When I wait, I can see, that firefox panes are updating, I can use the mouse,
but nothing happens on the screen.

I can login from remote and kill the Xorg-Process. After this I can start the
Session again and work.

Here is a stack trace of the Xorg Server:


-bash-3.2$ pfexec pstack 1428
1428:   /usr/X11/bin/Xorg :0 -nolisten tcp -audit 0 -br -auth /var/lib/gdm/:0.
-----------------  lwp# 1 / thread# 1  --------------------
 ceaf3465 pollsys  (8047010, 25, 0, 0)
 cea9d291 pselect  (ff, 8409590, 0, 0, 0, 0) + 199
 cea9d666 select   (ff, 8409590, 0, 0, 0, 8409590) + 78
 080c2c86 WaitForSomething (8a61290, 8206000, 8047c08, 80954bb) + 4f2
 0809508b Dispatch (840a4f0, 840a4f4, 8409a10, 840a990, 840a9c4, 82099b4) + e3
 080b104c main     (9, 8047d54, 8047d7c, 808975f) + 684
 080897bd _start   (9, 8047e24, 8047e36, 8047e39, 8047e43, 8047e47) + 7d
-----------------  lwp# 2 / thread# 2  --------------------
 ceaf42cf door     (0, 0, 0, ce10ee00, f5f00, a)
 cead9f27 door_create_func (0, ceb81000, ce10efe8, ceaee45e) + 2f
 ceaee4b3 _thrp_setup (c5d40200) + 9b
 ceaee740 _lwp_start (c5d40200, 0, 0, 0, 0, 0)
-----------------  lwp# 3 / thread# 3  --------------------
 ceaee799 lwp_park (0, 0, 0)
 ceae7d9d cond_wait_queue (8a66350, 8a66360, 0, ceae82c6) + 60
 ceae833e __cond_wait (8a66350, 8a66360, c5d3ef88, ceae8383) + 86
 ceae8391 cond_wait (8a66350, 8a66360, 200, ce2337e2) + 24
 ce233822 subscriber_event_handler (8a66310, ceb81000, c5d3efe8, ceaee45e) + 4e
 ceaee4b3 _thrp_setup (c5d40a00) + 9b
 ceaee740 _lwp_start (c5d40a00, 0, 0, 0, 0, 0)