хуже и не придумаешь

Doesn't work for Mr Robot Season 3 Episode 8.

The series is usually in 16:9 but in this episode, they made it 21:9. By throwing in good ol' black bars top and bottom.

There don't seem to be any instructions on how to make this add on work. It looks like it's trying to do it natively. If so, it's failing.

Funciona, sencillo y efectivo.

This works perfectly with youtube. It is exactly what I was looking for. I know stretching a 16:9 video to 21:9 looks a little bit odd but I prefer it to having black bars on the screen.

Great solution that works for me. The other ultra wide video add ons crop into the video and you you don't get the full image but this one does a good job of leaving the entire video visible and fitted for ultra wides.

Only note is that for me the aspect ratio and crop buttons on the top don't do anything, I have to press the force crop or force perspective buttons to get the add on to function.
I am using Firefox Quantum.