Recently I tested all audio addons, which were updated during the last 12 months. Among the better ones Waveform is the privacy champion: it requires the least severe permissions, by far! The UI provides technical infos, you won't get elsewhere - nerds will love it. Functionality is very good, but not perfect. The addon doesn‘t work on Bandcamp and Spotify. Sometimes it breaks live streams and mutes Dailymotion after reloading. In both cases, you‘ll have to start Firefox once again.

Great alternative to popular 600% volume addon that got banned. Works on YouTube, Twitch and Bilibili

So good! started getting lots of attention from the ladies after using this one!