Why does Safari quit when all tabs/windows are closed?
I've noticed that if I close all tabs/windows of Safari and I'm not using it for a time, when I click on it in my dock, I realize the application has quit. I prefer to stay in 'private browsing' permanently, but from time to time, when I'm using Safari, I don't realize that I had re-opened it and now I'm no longer browsing in private. Then I have to clear history, and reset safari and everything.
Can't seem to find a thread for this specific problem. My suspicion is that this is something Apple changed about Safari at one point, thinking it's a benefit, the way you close System Prefs and it quits the application altogether, you know, as an energy-saving feature. But this is really annoying.
Why is this happening? Can I fix it?
MacBook (13-inch), OS X Mountain Lion (10.8.4)