This may be caused by a recent Flash 11.3 update.

See:

• https://support.mozilla.org/kb/flash-113-doesnt-load-video-firefox

• http://forums.adobe.com/thread/1018071?tstart=0
• http://blogs.adobe.com/asset/2012/06/inside-flash-player-protected-mode-for-firefox.html

I had to uninstall real player. Then YouTube worked again.

Rolled back Flash to 10.3. No Real Player installed. YouTube loads in IE9 but does not load with graphics in Firefox 13.0.1 with Win7. See screenshot

H farci,

This thread is a solved thread. You would do better to ask your own question and start your own thread if the answers already given do not help you.

• use /questions/new and follow the prompts and links

Also note the issue described is under investigation, and so it may be worth revisiting any linked articles to check for revised advise and a more permanent solution.

Also see

• Flash Plugin - Keep it up to date and troubleshoot problems that is general advice - bare in mind that at present updating to Flash 11.3 on Firefox 13 may not in fact be a good idea
• Websites look wrong or appear differently than they should - your attached screenshot probably does not look as expected, do you have any other underlying problems

Djseeker2001's suggestion to remove Real Player has solved my problem with Youtube not playing on Firefox.

Yup, worked for me too: just removed Real Player and my You Tube clips are once again viewable through Firefox (I could still access them from Explorer, however). Easy fix--for once!