I needed something like this bad.
I have some bluetooth headset that has horrible treble, this addon seems to reduce it a lot. Hearing crackles in audio off youtube though not sure why

SURPRISING !!!

Doesn't work with Napster (streaming service) out of the box, unfortunately. Although neither does "Audio Equalizer and Amplifier," so maybe it's just Firefox not playing nice with my system.

Indeed works with HTML5 audio but unfortunately this doesn't work with music/radio extensions.

The equalizer works very well. However, I do not know what is the reason that after installing this add-on I stop playing movies on the pages (they only play on you tube and facebook). If you correct it, it will be the best addition in this category

QL !!!

Work very well. Tnx!!

Dose not work.
Each slider can move but sound is not changing at all.
Other Equalizing addons for Firefox dose also not work.
But same addons can work in chrome.