I just tested your login form and it appears to work fine from my end. Upon, hitting login, it takes me straight to the "My Profile" page displaying the email and the option to edit registered numbers.
Perhaps, because you have been developing it, maybe you need to delete the cache on your machine to get an accurate representation of what is happening, but it all looks good from my end (very nice site, too).
I am using Firefox 3.5.4 on Mac OSX 10.6.1. Not sure what other setups you have tested on, although, I doubt the kind of issue you were referring to would be browser specific.