And it is worth noting that the reason PIE is not enabled on Firefox on Mac OS X is because PIE executables are not supported on OS X 10.6, and Firefox still runs on OS X 10.6. Which won't be true in Firefox 49, due to release in 6 weeks, and that has PIE enabled (by the simple fact that MACOSX_DEPLOYMENT_VERSION was changed to 10.7 (the toolchain defaults to building PIE in that case), https://bugzilla.mozilla.org/show_bug.cgi?id=1269790).