For what it's worth, I had all my luck using Chrome. Firefox and IE(lol) wouldn't pull up the pages but I had all of them going at once.
Also, I logged into my Bitmain account 15 minutes before so my shipping info was ready to go.
Where did you put your address in on your account...I only see places to edit like
User ID
Mail
Subscription
No place to put address?
Can't even load the page right now but going off memory, lower left side of the user center page there should be a shipping or address link where you can add addresses and set your default.