Firefox has this now. I'm pretty sure it's standard.
RE: https://neckbeard.xyz/objects/3c1765eb-d54c-42bf-a09c-5c53c27ba6e5
Google chrome should have a mute button for each tab. -NlHILIST, Dec 2014
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@sergeantcat
This had been around for a long time now. I use it at work to mute ambience when I go into meetings.
@sergeantcat
Yes. Depending on the task at hand, I change what I'm listening to to out me into a different mental place. Sometimes I can't afford to let my coworkers know what I'm listening to for fear of job security. Othertimes I'm not the slightest concerned.
@lucifargundam@qoto.org can't let them know you're an anime theme song fan, right? 
@lucifargundam@qoto.org ambience? You mean ambient music?