--- a/build/moz.configure/init.configure
+++ b/build/moz.configure/init.configure
@@ -223,13 +223,32 @@ def include_project_configure(project, b
     if not project:
         error('--enable-project is required.')
 
     path = os.path.join(build_env['TOPSRCDIR'], project[0], 'moz.configure')
     if not os.path.exists(path):
         error('Cannot find project %s' % project[0])
     return path
 
-include(include_project_configure)
+@depends('--enable-project', '--help')
+def build_project(project, help):
+    return project[0]
+
+
+# This is temporary until js/src/configure and configure are merged.
+@depends(build_project)
+def extra_old_configure_args(build_project):
+    if build_project != 'js':
+        return []
+    return False
 
-@depends('--enable-project')
-def build_app(project):
-    return project[0]
+# Use instead of option() in js/moz.configure
+@template
+def js_option(*args, **kwargs):
+    opt = option(*args, **kwargs)
+
+    @depends(opt.option, extra_old_configure_args)
+    def js_option(value, extra_old_configure_args):
+        if extra_old_configure_args is not False:
+            extra_old_configure_args.append(value.format(opt.option))
+
+
+include(include_project_configure)

--- a/build/moz.configure/old.configure
+++ b/build/moz.configure/old.configure
@@ -55,20 +55,22 @@ def autoconf(mozconfig, autoconf):
 
     set_config('AUTOCONF', autoconf)
     return autoconf
 
 
 option(env='OLD_CONFIGURE', nargs=1, help='Path to the old configure script')
 
 @depends('OLD_CONFIGURE', mozconfig, autoconf, check_build_environment, shell,
-         virtualenv_python, compile_environment, build_app)
+         virtualenv_python, compile_environment, build_project,
+         extra_old_configure_args)
 @advanced
 def prepare_configure(old_configure, mozconfig, autoconf, build_env, shell,
-                      python, compile_env, build_app):
+                      python, compile_env, build_project,
+                      extra_old_configure_args):
     import glob
     import itertools
     import subprocess
     import sys
     # Import getmtime without overwriting the sandbox os.path.
     from os.path import getmtime
 
     from mozbuild.shellutil import quote
@@ -121,17 +123,20 @@ def prepare_configure(old_configure, moz
                 print("%s=%s" % (key, quote(value)), file=out)
             for t in ('env', 'vars'):
                 for key in mozconfig[t]['removed'].keys():
                     print("unset %s" % key, file=out)
 
         print('PYTHON=%s' % quote(python), file=out)
         if compile_env:
             print('COMPILE_ENVIRONMENT=1', file=out)
-        print('MOZ_BUILD_APP=%s' % build_app, file=out)
+        print('MOZ_BUILD_APP=%s' % build_project, file=out)
+
+    if extra_old_configure_args:
+        cmd += extra_old_configure_args
 
     return cmd
 
 
 @template
 def old_configure_options(*options):
     for opt in options:
         option(opt, nargs='*', help='Help missing for old configure options')

--- a/js/moz.configure
+++ b/js/moz.configure
@@ -1,12 +1,20 @@
 # -*- Mode: python; c-basic-offset: 4; indent-tabs-mode: nil; tab-width: 40 -*-
 # vim: set filetype=python:
 # This Source Code Form is subject to the terms of the Mozilla Public
 # License, v. 2.0. If a copy of the MPL was not distributed with this
 # file, You can obtain one at http://mozilla.org/MPL/2.0/.
 
-option('--disable-js-shell', help='Do not build the JS shell')
+# /!\ Use js_option() instead of option() in this file. /!\
+# =========================================================
+
+@depends(build_project, '--help')
+def js_shell_default(build_project, help):
+    return build_project == 'js'
+
+js_option('--disable-js-shell', default=js_shell_default,
+       help='Do not build the JS shell')
 
 @depends('--disable-js-shell')
 def js_shell(value):
     if not value:
         set_config('JS_DISABLE_SHELL', '1')

--- a/toolkit/moz.configure
+++ b/toolkit/moz.configure
@@ -1,5 +1,7 @@
 # -*- Mode: python; c-basic-offset: 4; indent-tabs-mode: nil; tab-width: 40 -*-
 # vim: set filetype=python:
 # This Source Code Form is subject to the terms of the Mozilla Public
 # License, v. 2.0. If a copy of the MPL was not distributed with this
 # file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+include('../js/moz.configure')