Have the exact same problem. Flash player opens in task bar as separate programm and the video is played essentially on the desktop, behind the taskbar. Problem occurs only in fullscreen, normal mode is ok. IE is ok, so there must not be a problem with Flash player (latest version). Problem occurs ALSO in Firefox safe mode, so it's a Firefox 7 related problem, no plugins, no themes, no dvxa etc. Tried about everything, disabled hardware acceleration etc., tried in F11 mode to no avail. Flash opens always separately than firefox 7. Major bug. OS win7 64

Hey this just started to happen to me today too; I just downgraded back to Firefox 6 and it started to work normally again. Here is the link let me know if anyone has found a fix so i can upgrade back to 7. Thanks

http://download.mozilla.org/?product=firefox-6.0.2&os=win&lang=en-US

https://support.mozilla.com/el/questions/880031#answer-259083

 The problem was solved by corduroy1979

That fix does not work with FF 9.0.1 :(

EDIT: Nor does it work with FF 10.0

EDIT: Also, my laptop has the same issue and doesn't use DPI.

I've just confirmed that this problem is actually with Windows 7, not with Firefox, and is present in several other programs, including VLC , Media Player and Chrome. I recently installed several Windows Updates, and once I locate which one caused the issue I'll post back.

EDIT: Sorry for the double post. I'll be sure and update my reply with the information once I've located it.