As many of you may be painfully aware, Firefox currently has a bug in that it doesn't shut down properly the first time and you have to force quit. Which can be a little irritating at times, particularly since Yosemite wont shut down until Firefox is. The good news is that I accidentally fixed it. What I did: While I was trying to drag my Firefox browser to a new space, i let it go while it was at the very edge of the screen (it has gone transparent, but hadn't crossed to the new space). The Firefox window disappeared (I had youtube on, sound was playing, but no window in any space). So I closed firefox and went back to the icon to Force Quit it and...it had already closed! I re-opened firefox, so my window came back, and then quit firefox again and it, again, shut down first time. Would like to see if any others can replicate this.