According to the analysis firm, Facebook counted 648 million unique visitors in November, which puts it ahead of Yahoo with 630 million, but behind Microsoft and Google.
ComScore also said that Facebook serves 23% of all online ads in the U.S. and provided videos to 58.5 million users, beating yahoo with 53.9 million. Google's DoubleClick ad planner was recently updated that also reflects the increase in traffic to Facebook. Google estimates that Facebook has about 600 million unique users and about 750 billion page views per month. Yahoo is listed with 410 million unique users and 70 billion page views.
In related news, securities firm Nyppex estimates Facebook's value now at about $41.2 billion. Yahoo has a market capitalization of about $21.4 billion.