I've just found your extension as I'm trying to watch things in order and, as you're aware, YouTube is terrible for this.
I was using PlaybackLoop but they've stopped that working too.
Is it possible to reverse just a playlist instead of all of the videos a channel uploads?
In my case I'm trying to catch up on the WoW pre-expansion videos but they upload lots of other videos too, when I pressed Alt+P my next video ended up being something I didn't want to watch, so I went looking for more information, or alternatives, and found out it just works this way.
I had pondered trying to use Tampermonkey to try but I'm not cluey enough to work that out. ๐ข