guys, you just can use an old version of the addon, v3.1.6 is still works for free on youtube and don`t mute tab.

addons.mozilla.org/firefox/downloads/file/4237766/audd-3.1.6.xpi

BUT, JFYI, song recognition on some sites, like twitch is PAID and on some other sites (like top-radio.ru) it is just dont working ("start error: can't find any unpaused media elements", its said)..