Google has introduced a referral program for AdSense publishers in an effort that's likely, at least in part, a response to Yahoo's encroachment on what Google sees as its turf. Google will reward AdSense publishers with $100 for each small publisher and blogger referred, paying the money after the new participants earn their first $100 in ad revenue, writes CNET. Google will also pay U.S. AdSense participants $1 for every person who downloads the Google Firefox toolbar via referral.