Try disabling the recently added autoplay blocking settings in Firefox. That could possibly be stopping the videos from playing, but I've had no issues using the sites referenced.

Otherwise, try running in Firefox Safe Mode to see if the problem continues in that mode. If not, it could be an issue caused by a browser extension or hardware acceleration.

Hope this helps.

Actually it was the whole computer.. Chrome wasnt working also nor and video player.. Shut it down and restarted it and sound was back and video... Ever since I put in a Samsung 860 EVOSSD been having problems lately and upgrading to El Captain and prblms when Firefox updated

I did try all that other stuff way before....

If you are having issues outside of Firefox as well, it's likely not a Firefox-related problem. You can try upgrading your graphics drivers to the latest version (if possible) and see if that helps.

Its not that everything is up to date.. I have a Mac laptop

Unfortunately, if the issue is system-wide, your question may be better suited for the Apple support website.