Firefox saves usernames and passwords for you in a Password Manager.  I'm not sure what IE does, but I imagine they have something similar.

Although your initial signup form correctly labels and names the form elements as email, username, etc... Firefox must go by the order of the input elements on the screen.  When it first saves your username and password it actually saves your email address and password.

Suggested fix: reorder the form elements to have:

email address

country

username

password

There is also a small character flaw in one of the country names that shows up as a <?> symbol in the dropdown list.  I didn't write down which country but it began with an S and has a weird symbol in it. =]

Awesome thanks, had no idea that was how FF managed passwords!

Also fixed the character problem, sorry if I offended any Saint Barthelemy residents :p