I don’t think I have it in me to put together a video, but I can describe it if you like.
Once you install the extension and follow the setup instructions, you just go to a YouTube page. The extension adds an ugly button to the top-left of the page that says “bypass”. When you click it, Firefox launches yt-dlp [the URL you’re at] -o - | mpv - which basically just downloads the video and streams the output through the mpv video player. So now you’re watching just the video, with no web page necessary.