And this is the pop-window it summons up.
Close it either by clicking on the at the top right-hand corner, or, if it is a larger window, by clicking on the message at the bottom.

    If this window is not about half the width of your screen (or of the notional ‘screen’ if your aspect ration is 16:9) and about a third of the height, and sitting in the top left-hand corner, you have probably failed to disable your pop-up blocker. Get instructions about this.

The same applies if the message below does not work: