Didn't work for me. As soon as I installed this add-on, I suddenly had no sound coming from Firefox. I pressed the add-on's buttons, I saw that it refreshed the video's page. But nothing. No sound at all. Maybe it's because I'm watching videos on BitChute, maybe it doesn't work with that.... i dunno.

Bonne extension depuis le temps que je voulais monter le volume merci. Cependant j'ai vu quelque chose lorsque je lance l'extension la page youtube redémarre, bien j'ai vu dans les critiques qu'il fallait redémarrer la page pour que ça marche et cela est fait automatiquement. Seul défaut à cette automatisation : il redémarre tous les onglets youtube même ceux qui sont en pause ce qui fait que toutes les vidéos se lancent en même temps

boost nothing

Does absolutely nothing! Does not work at all.

Does not work. Only 600% has worked for me but it has trouble when playing a new video.

it doesn't work

Refresh the page after you turn it on!

It does not work on Netflix, ive tried restarting the page, turning the extension on, off, turning it up and down, and all i got was my tab crashing, I also found the slider to be way too small

When active, Youtube video speed doesn't work.

It does work very well (the volume is correctly boosted), but as soon as this addon is added the playback speed is set to 100% and cannot be modified anymore. Removing this addon restore the ability to change the playback speed.
Tested only on youtube, firefox 88, mac (catalina).