If you’re running on Ubuntu 10.10 Maverick and could not get Youtube, hulu flash to work on full-screen mode on Chromium, Firefox, or other web browsers. You can try following codes in Applications -> Accessories -> Terminal to fix this problem.

sudo mkdir /etc/adobe
sudo su
sudo echo \"OverrideGPUValidation = 1\" >> /etc/adobe/mms.cfg

It is said that the problem has something to do with flash having hardware acceleration enabled, and it is always present on older computers, specially with laptops using Mobile Intel® 945GM Express Chipset!

Check on noobrescue.com and Ubuntuforums.org