I used Opera browser a lot. And there was a small option, but that was very usefull. If you had only 1 tab open and you click “X” button on right side on it, a new tab was opened automatically. But when you click “X” button on up-right side of the browser, browser was closed. That was the best thing, that I would see in that browser. That can’t be very hard to do in code, so please, add it 
. PS. Sorry for my bad english, I am from Poland.