EMarketer has redone its mobile ad spending forecast and has some very good news for Facebook.

The company is now projecting that Facebook will book $339.3 million in mobile ad revenue this year, $851.4 million in 2013, and $1.22 billion in 2014.

This is a switch from the thinking that prevailed for much of this year, when most researchers and analysts had expected Facebook's mobile ad revenue to come in between $45 million and $100 million. (EMarketer's estimate from three months ago had Facebook at $75 million in mobile revenue.)

But Facebook's Q3 earnings included $153 million in mobile ad revenue -- or 14% of its total -- which surprised some observers, and caused many to re-think their assumptions.

EMarketer projects that Facebook's share of the mobile display market this year is 18.4%, ahead of Google's 17% and Pandora's 12.2%. It will pull ahead to a 25.2% share next year, while Google's hold will climb to 19.6%, according to the forecast. Meanwhile, Twitter's estimated share this year is 7.3% and expected to rise only slightly to 7.4% next year.

EMarketer's report is a substantial revision to an earlier one it issued in September, where it predicted mobile ad spending would grow 80% next year. Today's revision expects a 180% increase, attributed largely to the early success of so-called "native" ad formats like Facebook's mobile news feed ads and Twitter's promoted tweets.

EMarketer also observed Facebook delivering more ads to mobile users in recent months.

[Facebook's mobile] ad product is integrated with the core user experience, and they've been able to deliver more impressions and avoid the trap of a small screen," said Clark Fredricksen, eMarketer's VP-communications.