The idea is a good one, but:

1: if you were able to change the frequency of the bands, like in a parametric EQ that you would see in Fruity Loops, that would be better, but that is not the biggest issue.

2: The module does not actually shut off the dry output and instead directs both outputs to the browser out, causing the signal to clip when, lets say, you want to do a moderate bass boost. The only way to not have it clip is to turn the preamp all the way down, but THIS DISABLES THE EQ. Therefore, it is completely useless at what it tries to do at least for me, I do not know about others. Maybe I am making a mistake in using it, but I do not think so.

3: And I almost forgot! The graphical interface lags out severely for me. Whenever I slide a bar too fast, it applies the change over the next two seconds, which is infuriating for someone who is trying to find the right balance in the frequencies by ear.

So yeah, Firefox, I hope you get a better equalizer.

EDIT: Actually I think the double-mixing phenomenon I was describing is a problem with Firefox itself, not this particular EQ. I just tried it with another similar equalizer and it behaved, well, similarly. I am also using Ubuntu, don't know if that has anything to do with it...

Was unable to save custom preferences, and while the presets worked fine, I disliked having to reload a video if I decided during play to equalize the sound. Finally uninstalled the app, as it was also keeping sound from playing on a non-YouTube site (I narrowed it down by reopening Firefox in safe mode to make sure that was the cause). Good app but seems to need work.

Whenever I try to watch steaming videos on cytu.be, this addon made it so no videos load.

As user friendly as the addon seems, it ran slow and made the audio sound distorted (in my case at least). I wouldn't use this for bass boosting any audio or music.

Broke audio playback on bandcamp.com

overall it's working as expected. but it's not compatible with YouTube 1.5x speed. When this plugin is enabled, Youtube plays at 1x speed no matter what speed you choose.

Has many frequencies to tweak. However, it reduces loading times for YouTube, other streaming broadcasters, and Prime videos on Amazon cannot load when it is enabled on my Windows 10 desktop. There is also similar, but less severe problems with Windows 7 desktop.