I don't know all the reasons why some sites won't work with FF (poor coding standards would be one guess), but if you want to be able to use FF with this site, the following should work:
In the address bar of FF type
Code:
about:config
and press ENTER.
Edit the value for general.useragent.override (or create it if it is not there) with this value:
Code:
Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; SV1)
Be aware that this sort of perpetuates the problem - because people are visiting their site, what incentive do they have to make it accessible by other browsers?