Viewing, from the prettyPhoto download: prettyPhoto_compressed_3.1.3/index.html
I'm on OS X 10.7.2, I've tried it in: Safari 5.1.2 Chrome 12 Firefox 8
In all three when I click the "API Call" link all I see is a blank popup. It has a title "API Call Image 1", but the image isn't displayed, nor the gallery navigation.