Surprised nobody already suggested some kind of mouse gestures extension. I use foxy gestures and once you learn a few gestures (starting with closing a tab and undoing it) it becomes hard to live without it!
Gesturefy is also a popular alternative.
Genuine question: How are gestures faster / more efficient than clicking a button, or using keyboard hotkeys?
Or is this mainly for notebooks, tablets and smartphones?
Compared to clicking a button I would say a lot faster as you don't have to move your mouse to start initiating your gestures.
It's maybe more marginal compared to a short key. Still your hand is already on the mouse ready to execute a gesture.
Personally I find it really convenient and for me it's the second most useful add-on after ublock. When using a browser on other computers that don't have these I find it really tedious and I am shocked at how much ad there is.