I assume the video plays for you on the YouTube site. If there is a problem with that, please start here: Fix video and audio problems on Firefox for Windows N editions.

Are there particular sites where you notice this problem?

For example, I have a YouTube video embedded near the top of this page:

https://www.jeffersonscher.com/gm/google-hit-hider/

Is the player area blank or does it show the player?

I have the same issue. It's happening on https://bringatrailer.com/listing/1967-chevrolet-nova/ At the bottom of the text it says "and a video of this Nova is shown below:" with a blank spot below and then the photo gallery.

I can watch the video on the YouTube site. In Chrome, the blank spot is filled by the YouTube preview picture and the link works.

thank you- -Dan Farmer

Hi Dan, I posted a reply in your new thread here: https://support.mozilla.org/questions/1201119#answer-1068279