Related Clues:

• D.C. Internet domain
• Web address ending, perhaps
• Main subj. of a constitution
• WWW address starter
• Surfer's entry, for short
• It often starts with 'http'
•     www bookmark
• State biggie
• Start of untold millions of addresses
• It may start 'http://'
• Its common extensions are the theme of this puzzle
• Online address start
• Dot follower, perhaps
• Net address
• Web site address starter