I have just put the test page on a web server. The URL is:
http://www.rba.gov.au/BC_Test/overview.jsp
As indicated by both Mordechai and Ben, you should really validate your code before asking for help. It is an easy, automated way of pointing out potential bug sources
In this case, you have given two elements the id of "nav". This does not comply with the W3C specs. 'id' is only to be used once on each page, whereas 'class' may be used repeatedly (or only once). The problem with your initial testing having been done in IE is that IE incorrectly allows multiple IDs. Try Firefox 0.9 or another compliant browser as your main testing browser and refer back to others (such as IE) for bug testing
I suggest that you follow these links and correct all errors (not too many, actually) to see if that fixes your problem :
http://validator.w3.org/check?verbose=1&uri=http%3A//www.rba.gov.au/BC_Test/overview.jsp
http://jigsaw.w3.org/css-validator/validator?profile=css2&warning=2&uri=http%3A//www.rba.gov.au/BC_Test/overview.jsp
Oh, and I also noticed that you use 'Ul' in your CSS code. Firefox (and I think, many other browsers) are case-sensitive. As such, 'Ul' is different to 'ul'. This may also cause you some trouble
Hope that helps!
Cheers,
Lachlan
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