[djaychela]

I've also found it useful when I want to create a re-sizeable video window to suit whatever else I'm doing, as it conforms to the browser size (I was doing this when I was watching FastAI lectures). As you say, much more pleasant!

[Phemist]

Yes! It also solves one of my pet peeves, really a first world problem. Watching 16:9, 1080p videos full-screen on my 32:9 screen lags my PC hard, on basically every video streaming site. The big black bars on either side of the video are apparently very expensive to render (firefox, ubuntu 20.04, ymmv). Theater mode exists on a few of these websites, but I would really like a more general solution. For now, with the help of @boriselec's plug-in, I am satisfied with the /embed trick for youtube.