Don't know if it is related, but I'm facing a plugin container hang and nouveau
seems to be guilty in some way.

Got this thread with gdb :

Thread 1 (Thread 0x7f4dd7b37940 (LWP 2961)):
#0  0x00007f4dd2294337 in sched_yield () from /usr/lib/libc.so.6
#1  0x00007f4dbff0ee41 in ?? () from /usr/lib/vdpau/libvdpau_nouveau.so.1
#2  0x00007f4dbff9eca5 in ?? () from /usr/lib/vdpau/libvdpau_nouveau.so.1
#3  0x00007f4dbfe019c1 in vl_screen_destroy ()
   from /usr/lib/vdpau/libvdpau_nouveau.so.1
#4  0x00007f4dbff073a1 in vlVdpDeviceDestroy ()
   from /usr/lib/vdpau/libvdpau_nouveau.so.1
#5  0x00007f4dc4c252a8 in ?? () from /usr/lib/mozilla/plugins/libflashplayer.so
#6  0x00007f4dc48871b5 in ?? () from /usr/lib/mozilla/plugins/libflashplayer.so
#7  0x00007f4dc4888000 in ?? () from /usr/lib/mozilla/plugins/libflashplayer.so
#8  0x00007f4dc4e167c8 in ?? () from /usr/lib/mozilla/plugins/libflashplayer.so
#9  0x00007f4dc4e1cf7d in ?? () from /usr/lib/mozilla/plugins/libflashplayer.so
#10 0x00007f4dc4e1ea6b in ?? () from /usr/lib/mozilla/plugins/libflashplayer.so
Cannot access memory at address 0x7ffff106a948

Or is it a flash plugin bug ?