When I go to that site (using Safari), I get the message:
*** Currently the A9 Toolbar runs only on Microsoft Internet Explorer 5.5 or above. We are working to extend the toolbar to other browsers. ***
When visiting using Firefox, I get a completely different page. They should change the message on the first page to mention Firefox too. Otherwise, if it weren't for this post on MacBytes, I would have no idea that it's compatible with Firefox.