Jeff Miller has a funny weblog but its URL of http://jeff_miller.blogspot.com isn’t quite right, according to the Internet standard RFC 1738. The host name in a URL may contain letters, digits, and hyphens, but not underscores (“_”).
If your URL is illegal, then browsers that comply with the standards — e.g., Mozilla — can’t display it. So if you’re setting up a site through Blogspot or some other provider, please avoid this mistake.