I’m getting a blank box in Firefox, although it plays in Edge. Only add-on I have is Ublock.
I would try clearing the browser cache to see if that fixes the problem.
Is Ublock blocking video ads? In Safari, my adblocker was blocking YouTube ads, but it wasn’t working so I got black boxes. I had to whitelist YouTube to stop it.
On the other hand, I had to stop using Firefox, too many little annoyances/bugs. I switched to Edge.
Clearing the browser cache didn’t help. I’ll have to figure out how to whitelist Quarter to Three. It is the only site that really affects me.
Edit…I just realized I already have Ublock turned off on this site. Youtube isn’t affected.
Time to ditch Firefox. They are laying off a 3rd of their work force since they are losing their contract with Google, so it’s only going to get worse.