I can't play true fullscreen videos on youtube with htmp 5 with firefox 12.0 I did however see that it IS possible to have true fullscreen(you don't see the borders of your browser.) but i don't remember the firefox version i saw it on.

Hi, Please also '''Disable''' the Flash plugin in '''Tools''' ('''Alt''' + '''T''') > '''Add-ons''' > '''Plugins''' and check. The full screen control would be on the bottom right edge of the video. [http://www.youtube.com/watch?v=DWGd3l3o-C4 eg.]

Hello. I disabled ALL flash player related plugins and I still see the borders of my browser when i full screen a video. http://imageshack.us/photo/my-images/534/html5r.png/ Here's a link of what it looks like.

Please also check in a [https://support.mozilla.org/en-US/kb/Managing-profiles new profile] after disabling Flash. If the new profile is okay, you can later [https://support.mozilla.org/en-US/kb/Recovering%20important%20data%20from%20an%20old%20profile?s=profile&r=1&e=sph&as=s copy the needed personal data] from the old profile. Firefox stores your personal data and settings in [http://kb.mozillazine.org/Profile_folder another location (profile folder)] separate from its [http://kb.mozillazine.org/Installation_directory files/folder]. A new profile would have the default Firefox settings in '''Tools''' ('''Alt''' + '''T''') > [https://support.mozilla.org/en-US/kb/Options%20window Options] and [http://kb.mozillazine.org/About:config about:config], and usually would also be empty of '''Extensions''' and themes ('''Appearance''') in '''Tools''' > '''Add-ons''', and their settings. Also, a new profile would have no previous stored website cache/cookies/data/preferences etc., ('''Tools''' > [https://support.mozilla.org/en-US/kb/Clear%20Recent%20History '''Clear Recent History''']). [https://support.mozilla.org/en-US/kb/Profiles?s=profile&r=2&e=sph&as=s Profiles Howto] [http://kb.mozillazine.org/Profile_folder_-_Firefox Profile Folder & Files] [http://kb.mozillazine.org/About:config_entries about:config Entries]