This obviously may not work for everyone but my fix came from disabling NoScript in Firefox. Credit goes to Zappo in another post for giving me this answer. When putting in credit card info on either the Mogstation or the Square Enix Account Management System and hitting next, if you don't see a little Global Collect animation play saying its processing the payment, something is blocking it. With the add-on up I was getting error 401/601 on both websites and with it off everything went through first try.

I don't mean simply allowing Square-Enix in the NoScript exceptions, you have to disable/allow all scripts globally for it to get through. Apparently Global Collect doesn't work well with the add-on.