A couple of changes needed at the time of writing from the usual build requirements.
Building a 64-bit Firefox on the Mac
With the release of Snow Leopard, Apple is really starting to push 64-bit programs. Firefox is working towards a 64-bit release but even though the bugs are all resolved, it won’t be shipping anytime soon. Here’s what I did to build a 64-bit LLVM version of Firefox. Important warnings follow the list!