I updated mac sierra and firefox to latest. I switch logins from my work account to my personal account (admin) and then I hear this audio. I close all my apps and log out of my personal account and still hear audio. At this point I think I've been hacked. I switch back to my work account closing everything except my browser. Then I see a youtube video playing and found the culprit. That is when I realize that audio played in firefox will play on other accounts! Does anyone else have this problem? Did firefox somehow circumvent security and does it have root privileges? I did install a youtube downloader and I see it pops up some app everynow and then because it said firefox changed the way they do audio streams. Is that related?