I'd switched to using YouTube solely within FireFox on mobile to block ads without needing to deal with ReVanced. The main problem I had was that the YT player within FireFox was missing the 'zoom to fill' in full screen feature for widescreen videos that were uploaded in a standard 16:9 aspect ratio with black bars on the top/bottom on a modern phone with a widescreen aspect ratio when horizontal. This extension is a hidden gem and fixes that perfectly by adding a well designed button to the top left of the player when in full screen (give it a second to load sometimes). Uncheck the box in extension settings for automatic enable to have manual control so you can only turn it on when you need it, and you're golden. I hope this is maintained by the dev - this extension is a lifesaver for 'cinematic' wide aspect ratio content still often uploaded in 16:9 like music videos, movie/game trailers, or short films.

awesome! this one automatically works on android!

After Searching Tons of extensions finally, have something that works also for 21:10 aspect. Thank You for your work.

Nicely fixes fullscreen issues on mobile when viewing in "desktop mode", although the settings dialogue is not available, so I can't set the default to keep aspect ratio. Not a huge deal you just have to click the icon on each video to fit to screen correctly, otherwise a bit of the bottom is cut off.

Works great on mobile, works just like the app!!!

this fullscreen addon for youtube doesnt play yt videos once thier clicked on

Was looking for an extension to watch cropped youtube video on my vertical screen, works great thanks

I finally found the add-on I was looking for for great YouTube, thank you very much.

Thank you. Works a treat.