Looking up RFCs is really painful because the first IP address that comes back is an IPv6 address:
I takes several minutes for the browser to timeout with that IPv6 address and backoff to the IPv4 address.
But I'm otherwise prepared for IPv6 as soon as Comcast enables it. in the picture below, notice that my Internet router is IPv6 enabled, and that I'm indeed talking to it from my desktop via its IPv6 address.
So, to fix this, I simply need to turn off the IPv6 feature of my home gateway.