Facebook uses a wide variety of technologies according to Wikipedia. It uses Javascript for the end user's perception and manipulation of the website. The backend programming languages cover things like Hack, PHP, C++, Java, Python, Erlang, D, and XhP. It also sues MySQL and HBase for it's database services.
It certainly uses much more than the average website, however it is a very large and complex website that has to server almost a billion users every day. It must be able to adapt and be modified in order to grow and expand to larger quantities of users and new features.
