https://www.techradar.com/news/firefox-will-finally-mute-autoplaying-videos-courtesy-of-new-update

While Google Chrome, Microsoft Edge and Apple’s Safari already have the option to mute sound on sites that feature autoplay videos, Firefox has been slow to follow suit, but it’s finally coming.

Mozilla promised to add the feature when it chalked up its product roadmap earlier this year, stating, "Firefox will provide users with a way to block video auto-play that doesn't break websites."