Everywhere we build a Mac app bundle we do so with the same chunk of make rules cargo-culted around the tree: https://dxr.mozilla.org/mozilla-central/rev/cc473fe5dc512c450634506f68cbacfb40a06a23/toolkit/mozapps/update/updater/Makefile.in#50 https://dxr.mozilla.org/mozilla-central/rev/cc473fe5dc512c450634506f68cbacfb40a06a23/b2g/app/Makefile.in#48 https://dxr.mozilla.org/mozilla-central/rev/cc473fe5dc512c450634506f68cbacfb40a06a23/browser/app/Makefile.in#93 https://dxr.mozilla.org/mozilla-central/rev/cc473fe5dc512c450634506f68cbacfb40a06a23/ipc/app/Makefile.in#33 https://dxr.mozilla.org/mozilla-central/rev/cc473fe5dc512c450634506f68cbacfb40a06a23/toolkit/crashreporter/client/Makefile.in#25 https://dxr.mozilla.org/mozilla-central/rev/cc473fe5dc512c450634506f68cbacfb40a06a23/toolkit/mozapps/update/updater/Makefile.in#51 https://dxr.mozilla.org/mozilla-central/rev/cc473fe5dc512c450634506f68cbacfb40a06a23/toolkit/mozapps/update/updater/updater-xpcshell/Makefile.in#21 https://dxr.mozilla.org/mozilla-central/rev/cc473fe5dc512c450634506f68cbacfb40a06a23/xulrunner/app/Makefile.in#52 Given that 99% of that is copy-pasted, it shouldn't be hard to factor it out to a common implementation and then define something in moz.build to enable it. The `repackage` rules there worry me slightly, we'll have to see how that factors into l10n repacks before tearing into it. As a bonus, we could probably have an flag in the */app/moz.build invocations to say "this is the main app bundle", and use that to make the app bundle the default install location instead of dist/bin, which we've wanted to do for a while.