Fullscreen Flash Videos not playing in Ubuntu/Fedora/Debian/Chrome/Firefox/insert-whatever-here when Compiz Fusion Effects are enabled

If the headline seems familiar to you… try this:

sudo mkdir -p /etc/adobe
sudo echo "OverrideGPUValidation=1" > /etc/adobe/mms.cfg

(source)
and restart any open browsers for it to take effect.

Adobe blacklists anything with SGI as GLX vendor string for GPU acceleration. Intel cards/drivers report this though. In combination with Compiz desktop effects = bad. So using above snippet fixed any fullscreen issues on my Lenovo Thinkpad T500 with Mobile 4 Series Chipset.