Recently I tested all audio addons, which were updated during the last 12 months. 1000% Sound Booster by username 32480 is a good, modern alternative to the „600% Sound Volume“-family of forks (e.g. lefriend, savva, 1fexd). In general it does the same, but the code is much slimer (33kb vs 84-115kb) and well made. An unusual navigation-permission is required, which may help on sites with multiple media frames. There are exceptions for Twitch, computerbase.de and daum.net - so 1000% Sound Booster does nothing on those sites, while other addons break them.