When you go full screen, the entire top menu bar and window controls scroll away, until you move your mouse pointer to that area.
I'd like to see that being available as an option even in windowed mode, perhaps with some minimal indicator in the very top of the window.
I want my Bookmark Bar, and I want to see tabs - but only when I move my mouse pointer to that area, then they could scroll down a la how they do it already in full screen. There are probably some challenges on how to make this user friendly.
Rationale behind this is that I often want no controls, but still want to have two or more browser windows open tiled on my screen. Right now, tiling 4 windows wastes a frankly astonishing amount of space on task bars, tabs, and the like.