This problem has been reported for years on FireFox and Chrome browsers. Developers have tried all kinds of hacks to work around it by resizing their content... scaling backgrounds differently from the body, etc.
There is no good trick that Boom Learning can do that wouldn't cause other problems. By moving the background image around, we would mess up alignment of other elements that are supposed to match the background. Things like button frames or fill-in-the-blank areas.
We recommend keeping important data out of the 3 pixels on the far right or bottom of the screen.
For the super geeky among you, coding resources about this problem: