Greasy Fork

It works for me, all except:

1. The like/dislike buttons disjoint a small bit (and remain in pill form), but especially so when using the "Return YouTube Dislike" 3rd-Party Firefox extension.
2. Video thumbnails still have rounded corners.

Others might note that the search bar is unaffected and the 'blacker black' background color is also unaffected.

this solves the thumbnails and maybe some other stuff, havent yet figured out the like/dislike btns

yt.config_.EXPERIMENT_FLAGS.web_rounded_thumbnails = false;
yt.config_.EXPERIMENT_FLAGS.web_rounded_containers = false;
yt.config_.EXPERIMENT_FLAGS.web_darker_dark_theme = false;