There are issues to fix with this, but really - nothing else offers this functionality on Windows. Not cash-grab WinStore apps, bash scripts, hacks, cracks - literally nothing.
The 'functionality' being this - video in a desktop window filling as much window real-estate as possible.
No comments. No awkwardly cropped videos because the window is too small. Window size = video size (or as close as it gets).
On a single monitor, you can dedicate a given portion of the screen to a small Firefox window, filled to the brim with distilled YouTube content, and use the remaining screen area to work on spreadsheets or whatever.
This is as much windowed video as you can get, having to put up only with Firefox title and scroll bars. Check this - you can key-in the precise dimensions of the video you want! Why is this not a feature of EVERY player???