Hello jricci9,

please be aware that Firefox 13 is currently in Beta and therefore, can and will most likely give you some errors and bugs, but this issue should normally be fixed with the stable launch of it. However, your issue seems to be due to some of the plugins in use on your system. Please check for updates on the plugincheck page and upgrade them if needed. If no updates can be found, launch Firefox with Add-Ons disabled and see if that fixes your problem. You can then remove the Shockwave Flash plugin and reinstall it from the Adobe website.

Thank you for your patience and please let me know how it goes.

I just installed FF 12 and it still does it...I'm investigating more...I will check plugins...other suggestions?

Hello jricci9,

as stated in an earlier reply, I would suggest you to run the plugincheck and see what it brings up and then try to launch Firefox in Add-Ons-disabled mode. If the problem still occurs, try to remove the Shockwave Flash plugin and reinstall it from the official website.

Ok, just updated all of the plugins, silverlight was the only one out of date. Still slow, SOME videos on youtube, not all. And here is more interesting info...I posted the video to my facebook wall and when played thru youtube via facebook the video is fine, but when viewed directly on youtube's page, the frame rate is slow. Does that help?

BTW, plays fine in IE on the same system!

I found the answer...in youtube when I right clicked on the video I selected LEAVE THE HTML5 test and that fixed it. So it's firefox and HTML5. I hope this helps you!

Hello jricci9,

thank you very much for your solution as it will surely help us troubleshoot some similar issues in the future.

Thanks a lot for all your valuable time and all your interest in Mozilla Firefox. Have a great day now!