Hiya
It looks like there is a layout bug in your SiteBox html template, which results in unnecessary scrollbars added to the iFrame. (Which could be a result of facebook perhaps having changed their layout since you have done the tutorials).
Which persist even after removing the Debug panel.
PS: Also I have a question about the whole iFrame setup? if you look at the facebook game CityVille: http://apps.facebook.com/cityville/
If you navigate the game through its tabs on the top, then when you leave the main game page, and maybe visit the help page, and then go back to the game, the game does not reload ? It just reappears like if it was running in the background, Like if its not a separate html page, but they are just pushing it off screen with CSS or javascript or iFrame magic? Any ideas ?
Firefox 3.6 - scrollbars at the bottom
IE7 - scrollbars on the right side ( these actually cut off part of the site )