Comment # 9 on bug 96737 from poma

Of course, the same with glx disabled

/etc/X11/xorg.conf.d/glx.conf
Section "Module"
        Disable "glx"
EndSection

/var/log/Xorg.0.log
(WW) "glx" will not be loaded unless you've specified it to be loaded
elsewhere.
(II) "glx" will be loaded even though the default is to disable it.
(==) NOUVEAU(0): GLX sync to VBlank enabled.

xfwm4-WARNING **: GLX extension missing, GLX support disabled.