Currently, firefox's (version like, 66.x.x?) blocking of autoplaying audio is inclusive of youtube, which is pretty annoying.Fix:open the hamburger menu on top rightclick optionsin options search at top, type "autoplay"you will see a checkbox with the text "Block websites from automatically playing sound"click the exceptions box for that optiontype "https://www.youtube.com" in to the text fieldclick allowclick save changesThat'll do it. via /r/youtube
