It seems a very good userscript, read: - YouTubeCenter Features - The last review in its Firefox Addon page (Extremely usefull: by LucasZ 23 March 2017 ): "This add-on improved functionality of my youtube by 1000%. VERSION IN MOZILLA STORAGE IS OUTDATED but developer version from it's website works just fine. All you need to make it work is Greasemonkey add-on (you don't even have to configure it, just install) before you install YouTube Center from here: https://github.com/YePpHa/YouTubeCenter/wiki/Developer-Version . It gives you so many options to customize your YouTube experience that you will never want to browse it without this add-on. Player resizing, page display customization, no chopped buffering! and many more. This is awesome"