yeah...I had a problem with that a while back. I guess firefox 3.5 is too "up to date." I think it's only compatible with 3.0 and below. So what you need to do is use internet explorer *shudders*. But if you have updated your IE, as well, you need to run it in the "backwards compatibility" mode (see the button right next to the search bar), since AMCAS is incompatible with the latest version of IE as well.
Yep, this happened to me too. You need to uninstall Firefox 3.5. Then google "older versions mozilla firefox" and download 3.0. Then, everything will work properly. AMCAS will not work on Google Chrome or the latest version of IE. If you have any trouble locating the browser, feel free to PM me.
You don't need to uninstall firefox. The easiest way I found was to use the "User Agent" extension with firefox. It allows you to use IE 7 which AMCAS accepts. https://addons.mozilla.org/en-US/firefox/addon/59