YouTube Fullscreen Fit от Dinoosauro

This extension permits you to make every YouTube video completely fit your screen when opened in fullscreen mode. Works with every aspect ratio.

From the extension settings, you can choose if you want to automatically enable the extension, or if you want to stretch the video instead of zooming it (and keeping the aspect ratio). You can always enable/disable the extension from the buttons at the right of the YouTube player.

NOTE: After installing, click on the extension and grant the authorization to access YouTube. Otherwise, the extension won't be able to resize the video.

This project is open-source. You can see the source code at: https://github.com/Dinoosauro/youtube-fullscreen-fit