It’s funny that this kind of browser extension has recurred over the years. Originally it was to replace the awful CPU hog flash player with an HTML5 h.264 player[1], then it was to sidestep YouTube’s insistence on VP* codecs, and now it’s to sidestep AV1.
In a beautiful world, there would be a link to each codec to let the user decide, or the browser itself would override the web site's preference and provide such links. It's sad that we keep having to resort to browser extensions to circumvent terrible web site and browser software.