Hmm. Works for me on a few different Firefox 1.5.0.2 boxen. How odd.
Hang on – how can you see an image that’s below the bottom of the page? Do you mean below the bottom of the window?
Some of the images are quite large; if you’re viewing at 800×600 the bottom of the images might appear below the bottom of a default-toolbar maximised Firefox window. But I’m not sure how you’d get the whole image to appear so low.
Ah well.