Before looking at new XUL tags, we briefly revisit the <window> tag. The window tag supports the following special attributes:
sizemode windowtype screenX screenY width height
sizemode applies only to the topmost <window> (or <dialog>) tag. It records the appearance of the matching window on the desktop. It can be set to normal, minimized, or maximized.
windowtype is used to collect windows of like type. This attribute can be set to any programmer-defined string. This attribute takes effect when two or more windows with the same windowtype are displayed. Mozilla will make an effort to ensure that when the second or subsequent windows are opened, that they are offset from the existing windows of the same type. ...