>>105768136You made me curious since Enhancer for YouTube does change the theater mode ratio for some reason. Apparently there are ways to do it, even with uBlock or with userstyles (such as Stylus, but you can probably make a monkey script as well). And a couple of extensions that allow fullscreen theater mode:
https://addons.mozilla.org/en-US/firefox/addon/youtube-high-definition/
https://addons.mozilla.org/en-US/firefox/addon/particle-iridium/
I can confirm the first one works, haven't tried the second one. As for the uBlock/Stylus stuff, I'm just gonna try to post the Reddit links.
https://old.reddit.com/r/uBlockOrigin/comments/1abqfya/full_screenfull_height_theater_mode_for_youtube/
https://old.reddit.com/r/userstyles/comments/aapem9/full_height_youtube_video_in_theater_mode/