prepend is an object not a message. replace the message box "prepend xfade" with an object box "prepend xfade".
get info on your hslider and change the range to 100.
remove all green matrix connections to the jit.window except the one from the xfade object.
everything works as expected after this.
if you mean how are you able to manipulate your controls when your window is in fullscreen mode, then generally the answer is you only go to fullscreen when you have a separate monitor or projector attached.