What should I do if I close my browser before my transaction is confirmed?
As long as you have the receiving address, you have nothing to worry about. All Bitcoin transfers will be automatically processed within the next 72 hours.

When does the receiving address expire?
All automatically generated wallet addresses are valid for 72 hours to prevent reuse. After the expiration of this period the address as well as all order details will be completely deleted, future payments to this address will be ignored.