FILE - A worker walks into Yahoo headquarters in Sunnyvale, Calif., in this July 29, 2009 file photo. Yahoo will supplant Google's search engine on Firefox's Web browser in the U.S., signaling Yahoo's resolve to regain some of the ground that it has lost in the most lucrative part of the Internet's ad market. The five-year alliance was announced Wednesday Nov. 19, 2014. (AP Photo/Paul Sakuima, File)