My extension allows you to customize the video quality experience based on the video's FPS (Frames Per Second). You can adjust the quality anywhere from 144p to 8K.
This means, for example, that you can watch 30FPS videos at 4K and 60FPS videos at 1080p!

You also have the option to automatically select the enhanced bitrate quality. Additionally, the extension lets you choose the quality of embedded videos, which are videos outside of YouTube.com.

Lastly, you can enable the auto-resize feature to adjust the video size automatically.

Source code: https://github.com/avi12/youtube-auto-hd