I'm sorry, but you have hit precisely the kind of browser incompatibility that sends me back to using tables for layout. I know that some people get very hot under the collar when you do that, but support for tables is better and more consistent than support for CSS - especially when it comes to floats, overflows, etc.
Whilst I'm looking at your website, there's one thing that I've noticed that is slightly irritating (sorry)! You knwo when you hoever over the menu items? The tab changes from having rounded corners at the top to having 90 degree corners. Maybe not everyone would notice that...