Video on Facebook using Safari

I'm on an iMac using Catalina 10.15.7

When looking at Facebook, if someone has included a video in their post it doesn't always show (just a black box where the video should be). If I Quit Safari from the Dock, and then relaunch, when it comes back the video will be there. This will be ok for a few days, then I have to repeat the process.

The same problem doesn't occur if I view FB using Chrome. That shows the video ok.

This has only started happening in the last few weeks.