Moreover, I always mute the speakers of my computer, for exactly that reason. When I do want sound, I usually connect my headset or an external speaker. The computer's speakers remain muted. In the rare cases where I do want to use the computer's speakers, I unmute them, and mute them when I'm finished. This is so seldom that it's not a big deal.
Back to browsers, I wonder why those implemented auto-play for videos in the first place. More specifically: I wonder why they auto-play audio, as I don't see that issue with animated GIFs. Moving ads are annoying, but not remotely as bad as an unexpected sound.
The upcoming Firefox versions are very promising in that regard:
"Block video auto-play: Firefox will provide users with a way to block video auto-play that doesn't break websites." https://wiki.mozilla.org/Firefox/Roadmap
"Implement new autoplay policy" https://bugzilla.mozilla.org/show_bug.cgi?id=1382574