No, they aren't.
Quote Adam D'Angelo, former CTO of Facebook: "PHP was out of the question [for building Quora]. Facebook is stuck on that for legacy reasons, not because it's the best choice right now". (source: http://www.quora.com/Quora-Infrastructure/Why-did-Quora-choo...)
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Actually Facebook agrees with me so much that they rewrote PHP as a C++ macro called hiphop, and no longer use PHP.
A specious comment - hiphop transforms PHP to optimised C++ and then compiles it.
Re:PHP Sucks But I Like It
by scriptproof on Wednesday April 11, 2012 @12:32PM
(#3828289)
Compilation = converting a language into another. Hiphop is a (two-stages) PHP compiler.
Facebook, Wikipedia are begging to disagree.