I have a lingering problem for a while now (at least last versions of Ubuntu).

Youtube (only youtube. Other flash vid sites I've tested are fine) videos aren't really full screen even in full screen mode. Video is displayed slightly larger than the original size with thick black border all around it on the rest of screen and the progress bar covering full width of the screen (as it does it full screen) right bellow the video.

My setup is Ubuntu Jaunty (same issue with Kubuntu), nVidia 7800 gtx with nvidia driver, dual-head, flashplugin-nonfree (version 10.0.22.87ubuntu2) on firefox 3.0.10 (right now but this issue has been there since I remember). I have also tried installing upstream tar.gz from flash's website but same result.

Googling suggests an issue of non-primary screen in flash plugin where the plugins doesn't give the video control of screen but I think that doesn't apply as this only happens with you tube. Other video sites work fine.

Anyone with similar issues or any ideas?