Comment 5 for bug 68554

I managed to get this to work by doing:
sudo gedit /usr/bin/firefox
and adding the following line as the second last:
export XLIB_SKIP_ARGB_VISUALS=1
After restarting firefox, it worked.

This is actually instructed in:
http://ubuntuguide.org/wiki/Ubuntu_Edgy#How_to_install_Flash_Player_.28Macromedia_Flash