Facebook is a company which is not exactly providing an open source software but delivering all those services in open source platform. According to the company they are believer in knowledge sharing and once they open their processes it will be good to design better model and more efficient perspective. Talented engineers will provide more and more inputs and it will make their recruitment process easier. Although the company is still not sharing any sensitive data, analytics processes and algorithms not because it will violate data security norms but it may create an integration problem as Facebook has a huge database. 12 years back Facebook started with an idea to use open source software to develop their own product and services and later they will make it available for open source development following the Google’s methodology.
To read, follow: http://www.forbes.com/sites/roberthof/2016/04/15/inside-facebooks-open-source-machine/#269823766e99