Here's a page that explains the process for each browser.
But it's not fool-proof, you have to block all of a certain kind of content, etc. etc.
For me, the answer was to assign a button on my mouse to be the Mute button. Many keyboards and mice have extra buttons that you can program to do things. Having a quick Mute button is really nice.
If you have a Logitech mouse, their mouse software makes it easy; you just pick which button you want to assign or re-assign, and you get a ton of different choices for what a mouse button can do.
(And I have the Performance MX which means I have like 10 different mouse buttons...)
(For those with a Logitech mouse, run the Mouse settings, select "Other" as a button task and you get 40 different choices, including copy/paste, undo/redo, play/pause, etc and one of the choices is MUTE. For those without a Logitech mouse, ask your local computer person for assistance in buying a new Logitech mouse on Amazon and installing it, along with their Setpoint mouse software. It's worth it)