I'm not sure if this a system wide error, but pressing the enter button to complete the address form freezes the page. The "continue to shipping" button will just try to refresh itself until you close or refresh the page. I tried this on several other shopify stores and the same thing happens. If you click the "continue to shipping" button with your mouse, then it proceeds are normal. But I figured this out fiddling with the checkout for sometime, and probably have already lost many customers who were trying to checkout.