X crash, xorg-server-1.20.12-x86_64-1 problem?

Seeing this error in a qemu guest (runs -current + XFCE) after upgrading to xorg-server-1.20.12-x86_64-1,
X crashes within seconds after starting youtube videos in Firefox.
Rolling back to 1.20.11 fixes the issue.
Host too is running the latest -current but has no issues.

Code:[ 1529.515] (EE) Backtrace:
[ 1529.515] (EE) 0: /usr/libexec/Xorg (OsLookupColor+0x135) [0x591985]
[ 1529.515] (EE) 1: /lib64/libpthread.so.0 (funlockfile+0x50) [0x7ff3fa411400]
[ 1529.516] (EE) 2: /lib64/libc.so.6 (gsignal+0x9b) [0x7ff3fa25badb]
[ 1529.524] (EE) 3: /lib64/libc.so.6 (abort+0x102) [0x7ff3fa242526]
[ 1529.525] (EE) 4: /lib64/libc.so.6 (__assert_fail_base.cold+0xf) [0x7ff3fa24241f]
[ 1529.525] (EE) 5: /lib64/libc.so.6 (__assert_fail+0x42) [0x7ff3fa253492]
[ 1529.525] (EE) 6: /usr/lib64/xorg/modules/libglamoregl.so (glamor_get_modifiers+0x2a3) [0x7ff3f99aafe3]
[ 1529.528] (EE) 7: /usr/lib64/xorg/modules/libglamoregl.so (glamor_egl_exchange_buffers+0x479) [0x7ff3f99abea9]
[ 1529.528] (EE) 8: /usr/lib64/xorg/modules/libglamoregl.so (glamor_gbm_bo_from_pixmap+0x1a) [0x7ff3f99abeca]
[ 1529.528] (EE) unw_get_proc_name failed: no unwind info found [-10]
[ 1529.528] (EE) 9: /usr/lib64/xorg/modules/drivers/modesetting_drv.so (?+0x0) [0x7ff3f9cd8d5b]
[ 1529.540] (EE) 10: /usr/libexec/Xorg (present_register_complete_notify+0x1a3c) [0x511bbc]
[ 1529.540] (EE) 11: /usr/libexec/Xorg (present_extension_init+0x499) [0x50e299]
[ 1529.540] (EE) 12: /usr/libexec/Xorg (present_register_complete_notify+0x2542) [0x5126c2]
[ 1529.540] (EE) 13: /usr/libexec/Xorg (present_register_complete_notify+0x1224) [0x5113a4]
[ 1529.540] (EE) 14: /usr/libexec/Xorg (SendErrorToClient+0x334) [0x43fc34]
[ 1529.540] (EE) 15: /usr/libexec/Xorg (InitFonts+0x3a4) [0x443ac4]
[ 1529.541] (EE) 16: /lib64/libc.so.6 (__libc_start_main+0xcd) [0x7ff3fa2441ad]
[ 1529.541] (EE) 17: /usr/libexec/Xorg (_start+0x2a) [0x42e19a]
[ 1529.541] (EE)
[ 1529.541] (EE)
Fatal server error:
[ 1529.541] (EE) Caught signal 6 (Aborted). Server aborting
[ 1529.541] (EE)
[ 1529.541] (EE)
Please consult the The X.Org Foundation support
at http://wiki.x.org
for help.
[ 1529.541] (EE) Please also check the log file at "/var/log/Xorg.0.log" for additional information.
[ 1529.541] (EE)
[ 1529.617] (EE) Server terminated with error (1). Closing log file.