lightbeam24

StarTube. Userscript for V3 that lets you choose your own YouTube layout.

CustomTube. Choose your own YouTube layout, plus some other settings!

AustralisFox. An Australis theme for modern Firefox.

youtube-watch-page-fix. Restores the old YouTube watch page

TubeK12. [DISCONTINUED] An attempt to recreate the 2012 YouTube layout using CSS.