You have three somewhat simple options for the search/url thing:

1) Have a single box, do not offer search suggestions. 2) Have a single box, offer search suggestions for the stuff users type in it. 3) Have separate boxes; offer search suggestions for the stuff typed in the search box but not the stuff typed in the url box.

#2 involves sending everything the user types in the url bar to the search suggestion provider to check for suggestions

Firefox does #3, because #2 is not considered acceptable from a user privacy perspective.

There are probably more complicated options here like only offering search suggestions if the string typed so far doesn't look like a URL or something that might protect user privacy better than a straight up #2. But it gets easy to screw it up and leak private user data to the search provider....