This does what it says perfectly but if you are trying to get a boarderless window to watch youtube videos it is now natively supported by firefox https://support.mozilla.org/en-US/kb/turn-picture-picture-mode so I would just that instead of this. This does what it says it does though and is very similar.

Excellent, has a hotkey and doesn't interfere with other youtube addons.

Exactly what i was looking for. Thank you!

Small & works well. Good combination.

This extension is critical for anyone with even the slightest sign of OCD, as the space YouTube wastes in "Theater mode" is UNGODLY, and the fact that the video is just barely larger than regular mode is a joke. Massive Thank You to whoever made this.

It will be extreme helpful if have auto target apply while playing.👍

For superultrawide this is a must have.

Unfortunately not reliable. Often times it requires a refresh of the page for it to even work. The hotkey works 50/50 and it honestly fails more than it works on both chrome and firefox

This is so good! YouTube should take this feature officially!

Nice extension if you use a Ultra-Widescreen!

Developer was super quick to fix an issue!!

The issues that was:
Recently (about 2-3 days ago) I noticed that when using Windowed FullScreen, the video cut-off (expands to fill the area) instead of having black bars.

its broke after youtube update :(
thx for the fix

Fantastic feature, but you need to refresh every single page once to get the button to appear.