Facebook's biggest challenge and its greatest opportunity now lies in mobile devices. Most Facebook users access it using a mobile phone or tablet computer, but the company only started showing mobile ads about 9 months ago.
Facebook said it generated 23%, or $306 million, of advertising revenue from mobile, up from 14% in the third quarter.
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The German bomb - a 500kg device - was spotted by a barge carrying out dredging works, the Royal Navy said.
The study found children born in the 1980s have found it much harder to build up wealth in housing and pensions as they age.
The singer ended speculation over who would perform by saying "the rumors are true" to her 63 million Twitter followers on Friday morning.