Can't see internet videos in fullscreen

[mintbox7]

I sometimes stream videos and it works good, but if I click fullscreen video the video just disappears but the audio is still working. On youtube its not working either it shows med midsize video but its somehow ruined.

I run mint 9 dvd amd 64 gnome, all updates (except upgrading to firefox 11)
No extra installed programs at all.
Firefox 9 I thought but it seems to be 11.
An old (at least 4 years) nvidia gfx and I have not installed any drivers or nothing for it, haven't touched anything.

Help.

What is wrong?

[mintbox7]

After restarting the computer I can now watch fullscreen videos but as soon as I shrink it the video freezes audio still running. what to do?

[mintbox7]

Actually on closer inspection nothing changed. I still can't stream fullscreen videos.

I don't know what is causing this but I'm guessing its one of these:
The browser
Some media player problems
Flash problems
Unknown

How do I revert back in versions of Firefox and flash?

How do i install a firefox version that is not in the repository? (from tar.bz2)
I only have 3 3,5 and such in the repository, and I know for a fact that firefox 7 would play fullscreen videos on mint 11 gnome.