On export C2 also passes <install path>\exporters\html5\c2-externs.js to Closure Compiler as a list of externs to not be renamed (see Closure Compiler's documentation on this). A few FB functions are listed there to guarantee they are not mangled by Closure Compiler.
Third party plugins can't edit this file, so just use the alternative syntax instead: rather than using FB.foo.bar(), use window["FB"]["foo"]["bar"](). This has the same result. A few official plugins take advantage of the c2-externs.js list simply for readability (so they can be written the first way and still not be renamed).