The milestone is important because it shows that Facebook is continuing to add users and provides a window into the social giant's strategy to scale in the fast-growing market sector.
Facebook's market share rose above $202 billion on Monday after the announcement, putting it on par with the world's biggest companies.
Earlier this year, Facebook engineers revamped its Android app to reduce its download size and decrease start times to make it more appealing to Internet users in developing countries, where devices limited memory was proving problematic.
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This announcement comes just a month after Facebook's Internet.org announced an app for Zambia that offers free access to Facebook and a dozen other services, including apps with health and employment services, Google, and Wikipedia.
Just last week, Facebook announced bandwidth targeting, helping advertisers develop the best mobile experience based on the connection.
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Facebook is investing to create tailored products for advertisers to tap into this fast-growing market, saying it's working with partners—that include Unilever—on tests of ad units based on how people connect with each other in different countries.