I've been using the "Mute sites by default" extension [0] for a while now and it does the job. 0: https://addons.mozilla.org/en-US/firefox/addon/mute-sites-by-

I've been using the "Mute sites by default" extension [0] for a while now and it does the job. 0: https://addons.mozilla.org/en-US/firefox/addon/mute-sites-by-default/ https://addons.mozilla.org/en-US/firefox/addon/mute-sites-by...