Any suggestions?

Any site featuring a streaming media player; not just Apple or WMP, but any player. I can watch it fine on the small screen or the 'resize' if it's available, but I cannot watch it on the 'full screen' mode. As soon as I click on full screen, my sound continues to play the show, but the screen goes white. I just had my computer serviced thinking it was a bug, but my I.T. guy says it's only with FireFox, that he could use the full screen options and see it fine with I.E. I have followed the suggestions from the help page and reset FF in my firewall settings... this had no effect. I've removed all addons and replaced them to no effect. I've re installed all flash players, to no effect. Any suggestions?