http://user http://user works for me on Firefox, directing me to user.com. However, when I look at the DNS requests, my DNS server says there is no such name as

http://user http://user works for me on Firefox, directing me to user.com. However, when I look at the DNS requests, my DNS server says there is no such name as "user". Right after that, a request is made for "www.user.com" then "user.com". I think Firefox is simply guessing the TLD in this case when just trying the name as provided fails and it's a TLD with no SLD (second-level domain). That said, http://ai http://ai does work at the DNS level. It's not that the domain has no TLD, but rather that the name is just the TLD.