Suddenly, Youtube won't play videos. It was fine just one day ago. When I click on a video, it comes up with a screen that looks very different and can't be activated. I never had this happen before. I am using Firefox. Is there a simple solution? I've tried turning off hardware acceleration in Firefox. It didn't work.

Have you tried rebooting your computer? Using a different browser?

Please try to describe this "screen that looks different."

YouTube is trying to force people to use their polymer version, which is slow and ugly.
I haven't had your exact problem, but you might want to try the "disable polymer" addon here
https://addons.mozilla.org/en-US/firefox/addon/disable-polymer-youtube/

Usually a Youtube video Has the enlarged box on the left to play the video of choice and a single column of other choices on the right. This one has a somewhat blurred choice on the left and two columns on the right, There is a play button, but it is inactive.

I'm using the new Edge browser and I don't see anything like that. I have a large screen on top with my video and under is a list of other options. In Firefox I have the same thing.

Jenny, how can you find out which version you are using. I looked as many places as I could think of and couldn't find anything. Whatever version I have - I very seldom watch Youtube - looks awesome with the big screen on top and is quite speedy.

I can get it in Edge just like it was before in Firefox. I have a bunch of maps and help videos that I use a lot with games. It would be handy to get them in Firefox. I don't think it is the polymer version causing the problem. I don't think it looks anything like what I have. It is strange, but my husband got the same unplayable video that I got last night. Today it is back to normal.

Did you ever try rebooting your computer?

Yes, I have. No change.

Very strange then... obviously something specific to Firefox.

Not that I know anything about this, but is your Firefox up to date? I'm not having any problems with YouTube using Firefox. I'm using version 77.0.1.

That's a good point, oldbroad. My version is the same.

That's also the version of Firefox I am using and I have no problems with YouTube.

Just checked and I have 77.0.1. Thanks for the input everyone. I'll report if I find a solution. There is hope since my husband's computer reverted back to the original Youtube.

Youtube is back. I deleted cookies and cache in Firefox history. After I did that, nothing seemed to work on my computer. I went into task manager and deleted Firefox and restarted my computer. Then I got a message about previous sessions of Google and Windows being not available, so I chose new sessions. That worked. I wonder if the computer was tied up deleting the history. I got no notice when I did it. Would those files be pretty large? It least my computer is back and Youtube is working again.

Good to hear! Frustrating when you can't get something to work, especially when it worked before!