Setting media.autoplay.blocking_policy to 2 seems to work, but I shouldn't have to do this manually just because Firefox updated.

I'd still like to know if the Troubleshooting Information field in the submission form actually did what it was supposed to.

There was no troubleshooting information send as that would appear if you click "More system details" in the side menu next to your question, so something went wrong.

See also:

• /questions/1293231 Block autoplay being ignored on Firefox 78

Edit: I had previously said autoplay blocking from the Preferences | Permissions for autoplay worked on one of my three PCs. Now it's not working on any of them, so my guess is that it's an intermittent issue as the OP wrote, and I just thought it was tied to the machines.

I use FF 83 on Linux, and as of this moment, it ignores the UI under Permissions that is set to Block audio and video (pref media.autoplay.default set to 5) on all of my machines.

I tried starting in safe mode and going to a video site, and this time, it blocked as it was supposed to. After I restarted Firefox, though, and disabled all the addons manually, one by one, it did not block autoplay. It would appear to be a pref that gets temporarily reset in safe mode.

After searching the web about the issue, I found this page, and I set the media.autoplay.blocking_policy pref to 2 as suggested, and indeed, it worked.