The redfly plugin is not immediately intuitative. You first do your search and then right click to do your country specific search.
What you have to do is that when you do your search, simply right click anywhere on the search results page and select “Search Google Global” and select the country of your preference from where you want the search results from. It is as simple as that.
This may still return results from domains outside those desired. The correct way to do this would be to include "site:" before the top level domain for example to search for .co.uk plumbing sites, you would use "plumbing site:.co.uk". Getting into the habit of adding this to your search string would probably be quicker than figuring out which button to press!