According to Opera's 'State of the mobile web' report, micro-blogging service Twitter was also popular with those viewing the mobile web last month. The number of unique users viewing Twitter jumped more than 2,800 percent from November.
Opera said more than 46.3 million people used Opera's Mini browser to access the mobile web, that's 11 percent up on November.
Furthermore 20.7 billion pages were viewed using Opera Mini, which is an increase of 223 percent compared to the same period the previous year and totalled 315 million MB of data.
Opera said its Mini browser compresses data by 90 percent, so if the data had remained uncompressed, Opera Mini users would have viewed over 2.9 petabytes (PB) of data in December.
"People want to use the same sites, regardless of whether they use a phone or PC to access those sites," said Jon von Tetzchner, co-founder, Opera Software.
"The success of Facebook and Twitter among Opera Mini users shows that consumer habits do not change even though their devices do."
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See also: Opera Mini use surges 11 percent