There used to be a little space at the end of the tab row, that you could drag a maximized window. After the last update it is gone. This is so frustrating.! Seriously in every update devs seems to look for more ways to make users move away from Opera.
@sgunhouse you confuse full screen with maximize window. In all maximized windows since win 3.1 you can click on the title bar and unmaximize / move the window. Of course this is happening to all other modern browsers too. They have a little gap between the end of the tab row and the minimize button for this exact reason.