[cpeterso]

Firefox's about:buildconfig page will tell you the compiler flags used to compile your Firefox:

  clang++ -Qunused-arguments -Qunused-arguments -Wall -Wpointer-arith -Woverloaded-virtual
  -Werror=return-type -Werror=int-to-pointer-cast -Wtype-limits -Wempty-body
  -Wsign-compare -Wno-invalid-offsetof -Wno-c++0x-extensions -Wno-extended-offsetof
  -Wno-unknown-warning-option -Wno-return-type-c-linkage -Wno-mismatched-tags
  -Wno-error=uninitialized -Wno-error=deprecated-declarations -isysroot /Developer/
  SDKs/MacOSX10.6.sdk -fno-exceptions -fno-strict-aliasing -fno-rtti -ffunction-sections
  -fdata-sections -fno-exceptions -fno-math-errno -std=gnu++0x -pthread -DNO_X11 -pipe
  -DNDEBUG -DTRIMMED -g -O3 -fno-omit-frame-pointer -Qunused-arguments