Moves the YouTube video to the top of the website and fill the window with the video player.
As of
After loading the video webpage you will see:
It appears above the rest of the site, so you can scroll down for the description, related links, etc.
https://github.com/Zren/ResizeYoutubePlayerToWindowSize/blob/master/changelog.md
about:config and set layout.css.scrollbar-width.enabled to true, then restart Firefox.