I would also like to know. I’ve been using Mullvad browser pretty much since it came out and I’ve always wanted to add the Libreddirect extension but never dared because of fingerprinting. I remember reading a while ago that on chromium browsers, some scripts can detect the mere presence of extensions. I have no idea if that could happen in firefow-based browsers as well.
Not a website thus definitely not what you’re looking for, but yt-dlp is a nice CLI tool to download videos/audios from YouTube and a lot of other websites in pretty much whatever format/quality you want. There are a multitude of mobile apps that bundle yt-dlp with a gui, I use Seal.