If you have problems with current Shockwave Flash plugin versions then check this:

• see if there are updates for your graphics drive drivers

https://support.mozilla.org/kb/upgrade-graphics-drivers-use-hardware-acceleration

• disable protected mode in the Flash plugin (Flash 11.3+ on Windows Vista and later)

https://forums.adobe.com/message/4468493#TemporaryWorkaround

• disable hardware acceleration in the Flash plugin

https://forums.adobe.com/thread/891337 See also:

• http://kb.mozillazine.org/Flash#Troubleshooting

Chakolate said

Youtube videos were playing fine in Firefox yesterday, but not today. I get a perpetual loading circle on a black screen. if i hover over the bar underneath it'll show me thumbnail captures of the video as i move my mouse across; similarly, if i drag my mouse while holding down, it'll show a horizontal grid of thumbnails superimposed over a bigger picture. Chrome plays the videos fine still, so I'm sure it's not a plugin issue or it'd be affecting Chrome also. Plugins are all up to date, for what it's worth. Was already using the most recent Firefox update before this, also. I copied the above from another questioner, because it exactly described the problem I have. I have cleared the cache and cookies, I have tried in Safe Mode, nothing helps. The videos play fine on Chrome. I installed an HTML5 addon, didn't fix the problem. Any suggestions?

Thanks!