Opera, the popular mobile browser, is dropping Yahoo as its default search engine for Google. While it hasn't had much success on the desktop, Opera is hugely popular in the mobile space, which many — especially at Google and Yahoo — consider to be the next big battlefront for search. Most users never change their default browsers and this is an good way for Google to expand its mobile reach. We don't know the details of any money changing hands, but given that Google search traffic sends tens of millions of dollars a year to Mozilla, the company behind Firefox, it's likely that Opera just enlarged their revenue stream a bit. Yahoo's been making a lot of noise about its mobile software suite. But Google makes more money per search. Code wins you flattering writeups in Wireless Industry Weekly Review. Dollars get you deals.