Firefox 3.6.3 is not supported by the Google Font API
I have Firefox 3.6.3 on my Macbook, but is only detected as 3.0.1on this form. When I link to the Google font website, it says, "We're sorry, but your browser is not supported by the Google Font API. To browse the fonts in the Google font directory please switch to a more modern browser." So I have to use Safari to get to the page.
URL of affected sites
Maybe this article will help - How to reset the default user agent on Firefox