To make it easier to grab the window and move it. You can maximize the window, and since you can't move it anymore once it's maximized, the tabs will move to th

To make it easier to grab the window and move it. You can maximize the window, and since you can't move it anymore once it's maximized, the tabs will move to the right of the Firefox button. This doesn't work on Linux, due to window manager issues. Perhaps Firefox can do something like Chrome does as a workaround, although Chrome's workaround is awfully heavyweight (it basically reimplements all the functions of the WM).