credit card form is very dark, and appears disabled. maybe lighten things up a bit?
Clicking add card takes you to the next screen, missing the promo field at the bottom, I had to deactivate my account in order to add the promo code I came prepared with. Perhaps moving the promo field up, or having a continue/next button for confirmation would make it easier.
FYI -> Firefox/25.0 on Mint KDE 15 AMD64