Mozilla wanted to expand the use of its Web browser, Firefox. Techies love Firefox, which is impervious to most viruses, but mainstream America hasn't embraced it. How does Mozilla translate innovation into market success? It turned to the "Creating Infectious Action" D-school class at Stanford University. Students prototyped Web sites and created a social networking site, Firefoxies.com, where users vote on the quality of friends' photos. The catch: You have to download Firefox to vote. So far, 30% of the site's visitors have done so.