A recent update for the Kindle Fire added an icon to the lower right corner of the browser window. This new icon (that looks like a little box with arrows at each corner) is used to enter full screen mode. Full screen mode hides the navigation bar at the bottom of each screen and the tab bar at the top. In full screen mode you cannot accidentally tap on the system 'Back' arrow and unexpectedly exit WIF 'n Proof. To exit full screen mode, slide up the arrow at the center bottom of the screen.
Helen