I use a window manager so I constantly have browser windows that take 1/2 or 1/4th of my screen. What annoys me is playing youtube videos in a 1/4 window – the top navbar scrolls as I scroll down so it covers part of the video. If I zoom in, the navbar gets larger as well. Full screen isn’t an option as well. What we need is a ‘full-page’ video player.
So I made minitube.surge.sh. (There are probably plugins that do this, but I like writing code.) The only selling point of this is that it's really lightweight.