All major browsers have a common feature : if you type something in the adress bar that is not a URL or the address part of a URL, a call to the preferred search engine is made. To do that, you have two choices :

  1. you check if the string in the address bar is a (partial) URL or not. That's not that hard. The number of TLDs is limited and we know how to parse URLs.
  2. you assume the string IS a network address anyway and ask the network layer of your computer to resolve it. If the answer is negative, then shmoogle it.

Of course, the latter has a higher cost. But the former deeply relies on the fact the list of TLDs is limited and well known.

Click in your address bar and type "qsdqsdqs.info" then press the return key. It looks and smells like a partial URL because "info" is a known TLD. FIrefox then tries to reach http://qsdqsdqs.info and that's what you were looking for.

Now the ICANN wants to entirely open up the list of TLDs. I will be able, in 2009, to register the "glazman" TLD !!! SO is the string "daniel.glazman" a web site's address or a string I am looking for through a search engine ?...