As the user that spotted it said, it has a "bleeding" effect on the background of the page. I've noticed this in Fx3 and Chrome.
Here is the code I used, along with the files from the demo page:
I don't really mind since I'm not using this script, I just thought you might want to know.
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd">
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
//Dynamic-FX slide in menu v6.5 (By maXimus, http://maximus.ravecore.com/)
//Updated July 8th, 03' for doctype bug
//For full source, and 100's more DHTML scripts, visit http://www.dynamicdrive.com