JJ90,
I still am baffled that the password fields don't work for you on that page. They are standard html password fields. There is some fancy design on them (note the hover color change) so maybe that is it.

So for an experiment, do the password fields on this page act normal for you?

http://www.guitartricks.com/register_free.php

Also, do you have any interesting FF addons installed?

Jon