It's simple: this extension mutes any audio and video sources it can find in your browser.

Why?

I was in a predicament. I would airplay music or white-noise at night, but I also liked watching videos on mute with closed-captions at the same time on my iPhone. This is just not an easy thing to work with, and I kept waking people up with videos that automatically unmute themselves, or especially with youtube that tends to follow the iPhone's system volume even if you try muting it over and over.

This extension helps with that as best as it can, to keep things quiet and under your control, so you can do whatever you want with your system volume.