See : https://developer.mozilla.org/en-US/docs/Mozilla/Firefox_OS/Platform/Gaia/Build_System_Primer
Also see : https://developer.mozilla.org/en-US/Firefox_OS/Customization_with_the_.userconfig_fileand https://github.com/mozilla-b2g/gaia/blob/master/Makefile#L489
==== Profiles ====
From kgrandon: {{bug|864751}}