As from windows applications to know which site?

C#. There is a program that must respond to open websites from a given list. How to know that the user in the browser?

You can search by window title, but this is not TRU.

You can read the url from the address bar (for ie process is described here — can to whom interesting), but it is necessary to know the names of the classes, but spy++ only in ie and chrome shows them.

Is there anywhere else?