Same here... Tab just stops responding and I have to close it. Started for me with 145. I have Nightly on another desktop with no account and no add-ons and it works. Also have a 2012 mac running 115ESR with all add-ons running and it also has no issues. You can also try downloading a different version of Firefox (Beta, Dev, or Nightly). Download, unzip, and run firefox-bin from the folder and see if you have the same issue. https://www.mozilla.org/en-US/firefox/channel/desktop/

Since I started having this problem, I have updated Windows, switched to Linux, bought a new PC (with more processor and more memory - there was some talk of it being a memory issue, which I would believe if Chrome, Chromium, Brave, Opera, et al didn't work PERFECTLY)

My new PC runs Linux (I see no reason to inflict Microsoft's AI on myself) and again Chromium works just fine. Firefox is a big ball of suck where YouTube is concerned.

I would believe that someone was interested in fixing this problem if anyone, had ever asked for more than the "Can you publish your troubleshooting data, so it looks like we actually care" question.

And it isn't video in general. It is only YT. Rumble works fine. Odysee works just fine.

Thing with Youtube is they are often making little and big changes and bugs can occur where they have to fix it on their end.

Chrome/Chromium browsers may seem to work in part because they come with codecs.

With Firefox and such browsers you may need to install packages like FFmpeg in order to fully use any HTML5 players used for videos, audio, games since the Flash Player Plugin is no longer used. Without packages like FFmpeg you may still be able to watch YT vids that have been up for a while but not live streams or recently uploaded videos.

So why is this not (to my knowledge) documented anywhere? (And why have I - and others - had problems for months and it was never mentioned?)

So is this the FFmpeg Firefox extension (which hasn't been updated in 2 years) or the FFMpeg Linux package?

I installed the codecs when I installed Linux, because otherwise VLC can't handle some video formats.

When I installed Linux, with an NVIDA GPU, the install script asked, "Do you want to be an open-source snob, or do you want to install the proprietary Codecs so you computer will actually work?" Firefox could do the same, and I would say, "Yes, install those evil proprietary codecs so that Firefox isn't a great big ball of suck."