Dev channel update to 75.0.139.4 is live

David Rubino -- #autoplay policy doesn't seem to be working consistently. I've set it to "Document user activation is required" but still get content playing sound on the page w/o my interaction. It's a mixed bag as some content will play w/o sound but others just crank right through the speakers. Sure will this feature would work as a "mute all;all the time".