Ok, here's something I noticed that could lead to someone finding the white button.
If you click anywhere in the text above the flash-window, where it says "Whatever you do, do not press the red button......etc" then hit the Tab key, a yellow square forms around the red button.
This is due to the button being an interactive component in the animation. If you do the same thing where there are multiple buttons on the screen at once, it will cycle through the buttons, highlighting them in yellow one at a time.
My theory is that on *one* slide, there will be a white button, which would be visible by using the tab feature. However, Í'm affraid I don't have the patience to try this :P
Goodluck to anyone with enough time
Dave