Nothing has been changed on my PC that I know of, but suddenly youtube videos won't play, even ones I have viewed before. This has been within the last 48 hours.
Please check if all your plugins are up-to-date. To do this, go to the Mozilla Plugin Check site.
Once you're there, the site will check if all your plugins have the latest versions. If you see plugins in the list that have a yellow Update button or a red Update now button, please update these immediately.
To do so, please click each red or yellow button. Then you should see a site that allows you to download the latest version. Double-click the downloaded file to start the installation and follow the steps mentioned in the installation procedure.
The latest Flash player for Firefox on Linux is 22.214.171.124.
Start Firefox in Safe Mode to check if one of the extensions (Firefox/Tools > Add-ons > Extensions) or if hardware acceleration is causing the problem (switch to the DEFAULT theme: Firefox/Tools > Add-ons > Appearance).
i guess i have the same problem. ubuntu 10.04 64 bit i up graded through automatic up dates from firefox 18.0.2 to 19 and my you tube videos no longer work now on another system i have not up dated yet and it is running firefox 18.0.2 and you tube works fine
after installing flash-aid i still had the same problem, so process of alimation and found it is download helper causing the problems. everything look ok when it is disabled
It seems that it is a problem with AdBlock extension. Maybe youtube blocks AdBlocked browsers????