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.