--- a/build/moz.configure/init.configure
+++ b/build/moz.configure/init.configure
@@ -223,22 +223,30 @@ def early_options():
             option.env
             for option in __sandbox__._options.itervalues()
             if option.env
         )
     return early_options
 
 early_options = early_options()
 
-@depends(mozconfig, '--help')
+@depends(mozconfig, 'MOZ_AUTOMATION', '--help')
 # This gives access to the sandbox. Don't copy this blindly.
 @imports('__sandbox__')
 @imports('os')
-def mozconfig_options(mozconfig, help):
+def mozconfig_options(mozconfig, automation, help):
     if mozconfig['path']:
+        if 'MOZ_AUTOMATION_MOZCONFIG' in mozconfig['env']['added']:
+            if not automation:
+                log.error('%s directly or indirectly includes an in-tree '
+                          'mozconfig.', mozconfig['path'])
+                log.error('In-tree mozconfigs make strong assumptions about '
+                          'and are only meant to be used by Mozilla'
+                          'automation.')
+                die("Please don't use them.")
         helper = __sandbox__._helper
         log.info('Adding configure options from %s' % mozconfig['path'])
         for arg in mozconfig['configure_args']:
             log.info('  %s' % arg)
             # We could be using imply_option() here, but it has other
             # contraints that don't really apply to the command-line
             # emulation that mozconfig provides.
             helper.add(arg, origin='mozconfig', args=helper._args)

--- a/build/mozconfig.automation
+++ b/build/mozconfig.automation
@@ -26,8 +26,10 @@ if test "$MOZ_AUTOMATION_PRETTY" = "1"; 
     mk_add_options "export MOZ_AUTOMATION_PRETTY_PACKAGE_TESTS=${MOZ_AUTOMATION_PACKAGE_TESTS-1}"
     mk_add_options "export MOZ_AUTOMATION_PRETTY_L10N_CHECK=${MOZ_AUTOMATION_L10N_CHECK-1}"
     mk_add_options "export MOZ_AUTOMATION_PRETTY_INSTALLER=${MOZ_AUTOMATION_INSTALLER-0}"
 
     # Note that we always build the update packaging with pretty names even if
     # we don't build it without, so this is set to 1.
     mk_add_options "export MOZ_AUTOMATION_PRETTY_UPDATE_PACKAGING=1"
 fi
+
+export MOZ_AUTOMATION_MOZCONFIG=1