Hum. On a Mac ... Using Chrome, the IPv6 test never starts, it just sits there after the IPv4 test completes. Tried multiple times. Safari works ok.
Windows 8 - Firefox 24 (not private or anything) and it stalls on the IPv6 test as well. Admittedly I am doing this from Charter and using a HE IPv6 tunnel so maybe that has something to do with it.