Works and has a gorgeous simple interface.

Funcionó fantástico en Firefox for Android Nightly. Ya no tengo problema al visualizar cualquier video.

UtraWimeo is the only one that actually works, I tried many other addons and wasted a lot of time for this. If this didn't work, I would need to be spending money for bigger monitor on computer I rarely use. Email answer was great also. This plugin is also private, nothing is sent out of computer.

Thanks, this fixed youtube cropped videos in fullscreen landscape mode

I'm using this with a 4:3 CRT and it's amazing. Works on HBO, Youtube, everything I've tried so far. Great for old 4:3 movies and videos that were uploaded with forced 16:9 pillarboxing, to put them back in fullscreen like they should be.

Работает нормально. При случае, когда очень хочется, всегда можно пожертвовать кусочком экрана 16:9 сверху-снизу, чтобы растянуть изображение на полный 21:9 экран

I'm using it on my Samsung Galaxy A51 (Android 10) after the top and the bottom from YouTube-Videos was cutted and it works perfect! Now I can watch YouTube-Videos completely, from top to bottom! Very good work!I really hope, this Add-On will be supported at the new Firefox for Android and Firefox Nightly!

Works for Amazon Prime Video. Thanks!

Thanks to the creators! Wanted this for Amazon Prime Video, and it worked!

I started using this after ultrawidefy stopped working for me. This does exactly what I need it to do on a 21:9 monitor, thanks!

Fonctionne parfaitement pour YouTube sur navigateur avec un écran 18:9. Plus de crop sur les bords haut et bas. L'extension a un paramétrage simple et efficace.

Это расширение работает!

Amazing work! Allows me to use my old widescreen tv with vga pc resolutions.
My one issue is the resolution doesn't change in twitch.tv theater mode, only on full screen.
Thanks dvlden, you rock! :)
edit: You're right! I'm use to the wide aspect in theater mode since originally writing the review. This addon is the best!

This works great on almost every video player, except Disney+. When I try to watch something, the video gets pushed down so that it only covers half the screen. If the developer could fix this, I would really appreciate it.

*Second edit* Issue seems resolved as of early April 2020. No idea what changed and I don't care hehe. Back to a 5/5 for me. *edit*

This add on is great, but it has a very annoying flaw. It randomly stop working (with some frequency), forcing me to go into the addon configuration and disable/re-enable it to get it to work again. It does exactly what it says it will do, which is awesome, but this erratic behaviour keeps it a 3/5 for me.

*first edit* I can't figure out how to reply, so I'll edit here. Interference may be coming from one of two add-ons I have: 1) uBlock Origin and 2) Video Background Play Fix. Of the two, background play seems more likely, but who knows. Unfortunately, I need those add-ons more than this one, so I'll just live with enabling / disabling for now. Also, I just assumed this was a Firefox for Android reporting / reviewing system, but it seems it isn't. Because I didn't mention it before, I'm running Android 9 on a Samsung A8 (2018). *edit*

I am using old samsung tab s 8.4. Maybe it has peculiar aspect ratio because all of my streaming videos has black bar on top/bottom. Few years of streaming videos this way has made my screen to have light burn-in (top/bottom brighter than the rest. Right now only detectable using screen diagnostic tool software). I don't want this problem to get to a point where it is clearly noticeable.

Tried everything, and this is the only one that worked on all of my streaming sites by force-stretch the video to full. Genius work !