There's no recent payment activity on your account, so it looks like a browser-related issue. When filling out the checkout form, can you see the cardholder name field?

Gah, sorry about not checking back earlier. It's a website layout glitch, I think it appeared as soon as Firefox 21 was released. If the Checkout page is scaled (by increasing the font size in the browser, or a system's DPI setting), the layout can go out of alignment. Resetting the zoom by pressing Ctrl-0 in the browser and/or switching DPI back to the default value (96 DPI or 100%) should solve the issue. Other browsers shouldn't be susceptible to this issue, as far as I know.

Our webdevs should be able to sort this out soon. Sorry about the issue.