Yeah, Arora is basically a browser demoing Qt/WebKit. I figured out why the disparity, though: if I turn down the font size in Safari or Opera, the problem turns up.
E] Seeing as you use fixed pixel quantities for positioning and the like, I'd recommend setting the font size via a pixel size, not an em size, as em sizes are relative to the browser's set font size, and by no means absolute like the rest of the website is.