I don't have any trouble getting you code to work in any browser that I have, and that includes Firefox. What I do have a problem with is if I have a doctype declaration of an XHTML document, the scripts stop working. Even if I put //<![CDATA[ and //]]> around the script and get the file to validate, it doesn't work. If I take the doctype out of the document and save it as html, then the script works. I would like to use validating xhtml. Any thoughts on why the script isn't working in an XHTML document with a doctype would be appreciated.

Check out this thread:
http://p2p.wrox.com/topic.asp?TOPIC_ID=43315

Try downloading that new version + the following CSS

html, body { height:100%; }

/José Jeria