Facebook has surpassed Yahoo to become the leading publisher of display ads in the U.S. according to a new report from comScore. In the first quarter Facebook delivered 176 billion display ad impressions, representing 16.2 percent market share. Yahoo sites ranked second with 132 billion impressions (12.1%), followed by Microsoft sites with 60 billion impressions (5.5%) and Fox Interactive Media with 53 billion impressions (4.9%).