Greasy Fork is available in English.
Maximizes the YouTube player to fill the entire browser viewport when in theater mode, plus a few other enhancements.
If you are still reading it: delete the 180 - 187 rows. That's it.
(Do not delete after that, though it is confusing as the comment looks like refers the following lines either...)
The author is probably not maintaining this script anymore, but it still works well.
Great scrip but is there a way to disable the "Expands the video description." is there a line I can disable or delete??