AdBlock Plus (ABP) has caused that problem on Youtube in the past. I do not experience the problem with youtube with ABP active. You can test by:

1. opening youtube in a tab
2. click the ABP icon and choose "Disable on this page only"
3. try to play some videos and see if youtube now works for you
4. If that does not work, before you leave the youtube page, once again click the ABP icon and click "Disable on this page only" to remove the check mark, then close the youtube page/tab.

Tried your suggestion, no effect.

Video doesn't play, same message displayed: "An error occurred. Please try again later." However, it plays in Google Chrome.

Helper7677 got me thinking and checked the cookie permission for youtube.com and saw that session cookies were permitted.

Blocked all cookies for youtube.com and tried again.

With all cookies on youtube.com blocked, youtube videos are displaying and playing, both embedded on other sites and on youtube.com.

Hope this helps others experiencing the same problem.

Thanks for posting and letting other users know of the solution that you found.

Would you post the step-by-step that you used so that other users can follow. I assume it was by changing the Page Info Permissions.

Sure.

Right-click on any www.youtube.com page - not on a video - and select ' View Page Info'. Under 'Set Cookies' select 'Block.'

or:

If using a cookie managing add-on, such as CS Lite https://addons.mozilla.org/en-US/firefox/addon/cs-lite/ follow the procedures of the add-on to block cookies while on any www.youtube.com webpage.