For some reason when Coffeecup HTML editor opens it starts with a small screen, when I click on the open full page in the top right bar it moves to the center of the screen then click on it again gets the desired effect of full screen.
Never used to do it but now it does and it,s most annoying.
Anyone any idea,s, I haave tried the preferences but to no avail.

Try resizing the smaller window by grabbing the edges to the way you would like it to be in this mode. It will remember your choice.