I actually use this one a lot, lets you take a video and make it the full size of the browser. I find that theater mode youtube isn't quite big enough on a 4k s

I actually use this one a lot, lets you take a video and make it the full size of the browser. I find that theater mode youtube isn't quite big enough on a 4k screen, but I don't want to pop into fullscreen mode. https://chrome.google.com/webstore/detail/fullscreen-video-to-windo/mkdkhflndckmdlpiaddfmpppmodplheo https://chrome.google.com/webstore/detail/fullscreen-video-t...