Chapters site is too busy to response

 

I got an email from Chapters Indigo Online. You know I made an order yesterday afternoon. I ordered two books.
1) Search Engine Visibility
2) Professional Search Engine Optimization With Php: A Developer’s Guide to SEO
The email said the confirmed order has been shipped. It is such a good news. The speed is so fast.
I would like to check the status of this shipment with the tracking number.
When I click the link it provided, it gave me the following error message.
error-chapters

Does it mean the Chapters’ business is too good? Their website can not afford such many users at the same time?
Or
The site is broken by some hackers?
I am scared about the later one.
All user’s information should be kept safely, including all credit card information.
Update:
It is only happen under Firefox. IE is OK.