
To clarify it happens when i scroll through a page. The videos it self play fine.

Bump.'[R-COM wrote:MaSSive;1783930']Found solution. Well it works for me.
Play some flash video on youtube. Right click on it and go to Settings. On first tab - Display - untick "Use hardware acceleration".
Open Options > Advanced > General tab in Firefox. Untick "Use hardware acceleration when available".
Restart Firefox and clear your browser cache. Tada.
With the latest flash update and on firefox 13 when I scroll on pages with youtube videos or other flash content it become corrupted. | Firefox Support Forum | Firefox Help