[SOLVED] Firefox and youtube-videos

I have get some problem to see videos in Firefox (7.0.1).
When I open the following link (http://www.seniornet.se) there will be 3 black areas, places for videos from youtube.
When I look att the page with Opera and IE9 it will show pictures and it is possible to start the video.
I have also the same problem with Firefox at other pages.
In these cases the video are at Youtube but Ithink the problem exist att other sites as well.
I don't understand where Firefox fail to show the video.
When I open the following link (http://www.seniornet.se) there will be 3 black areas, places for videos from youtube.
When I look att the page with Opera and IE9 it will show pictures and it is possible to start the video.
I have also the same problem with Firefox at other pages.
In these cases the video are at Youtube but Ithink the problem exist att other sites as well.
I don't understand where Firefox fail to show the video.