The reason it doesnt work is that "igo" is the name of another alias.
If you look at the igo alias itself (in the Core-Internet alias file), you'll see it uses the special command "htmlviewurl".
So, change your alias from "igo http://ninjawords.com/?q=
to something like "Search Ninjawords for $$1 | htmlviewurl http://ninjawords.com/?q=
That assumes you want the web page to open up inside of the FARR window. If you wanted it to open your external web browser you could just leave off the "htmlviewurl" part.