Clear the cache and the cookies from sites that cause problems.

"Clear the Cache":

• Tools > Options > Advanced > Network > Offline Storage (Cache): "Clear Now"

"Remove Cookies" from sites causing problems:

• Tools > Options > Privacy > Cookies: "Show Cookies"

Start Firefox in Diagnose Firefox issues using Troubleshoot Mode to check if one of the extensions or if hardware acceleration is causing the problem (switch to the DEFAULT theme: Firefox (Tools) > Add-ons > Appearance/Themes).

• Don't make any changes on the Safe mode start window.
• https://support.mozilla.com/kb/Safe+Mode

See also:

• http://kb2.adobe.com/cps/409/kb409116.html (Troubleshoot, report Flash Player video playback issues)

Try to disable the hardware acceleration in the Flash Player. See:

• https://support.mozilla.com/kb/Cannot+view+full+screen+Flash+videos
• http://www.youtube.com/swf_test.html (right-click the player: Settings)

Flash "Display settings" window:

• http://www.macromedia.com/support/documentation/en/flashplayer/help/help01.html

I have mac OS 10.6.8. Recently, youtube videos won't play. screen is black. i have loaded and unloaded and loaded flashplayer ad nauseum. if the problem is solved elsewhere (not on youtube), youtube remains unhappy with this exception: SOME videos MAY load but MOST DO NOT.

Fix needed, please!

And i have done the cache and the cookie solution. we are on round 3 now. i suspect a bug. ?