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That's up from 62% from a year ago.
The company's been heading this direction for some time - last quarter, 73% of its ad revenue was mobile - but it's still pretty stunning given that when Facebook went public in 2012, its mobile ad revenue was zero.
It's also pretty remarkable given the struggles other big media companies have had earning mobile ad revenues - Google just today started incorporating search ads into the Google Play Store, where users buy apps and content for their Android phones.
According to April research from Goldman Sachs, Google made about $12 billion in mobile search ad revenue last year - about 20% of its total ad revenue - and most of that came from search ads displayed on rival Apple's phones.