Actually, I think they need more than the red, yellow, green buttons. I think they need a button dedicated to this function, but not the green button, because people expect that to maximize it.
...and once the window has been maximized and one wants to return it to a smaller size? What then? It only stands to reason that the button that maximizes a window will also minimize it back down; otherwise it would be maximizing in perpetuity. The green button was correct before the alteration; it maximized the mini-player into a full-sized player, and minimized the full-sized player back into a mini-player. No 4th button is needed. What's needed is a fix to this; it seems like a small glitch, but it's actually quite annoying.