Yahoo to replace Google as default U.S. Firefox search engine by Reuters @FortuneMagazine November 19, 2014, 5:40 PM EST E-mail Tweet Facebook Google Plus Linkedin Share icons (REUTERS) – Yahoo Inc YHOO said on Wednesday it struck a deal to be the default search engine on the Firefox web browser on desktop PCs and mobile devices in the United States, replacing market leader Google Inc GOOG . The deal between Yahoo and Firefox maker Mozilla Corp will start in December and is set to last five years, Yahoo said. It was not immediately clear how the agreement will affect Yahoo’s existing arrangement with Microsoft Corp MSFT , whose Bing search engine currently powers Yahoo’s web search capabilities. Firefox had 10.4 percent of the U.S. browser market on desktop PCs, mobile smartphones and tablets last month, according to tech data firm StatCounter. Google’s Chrome browser was the leader with 33.5 percent.