--- a/b2g/app.mozbuild
+++ b/b2g/app.mozbuild
@@ -7,10 +7,9 @@
 include('/toolkit/toolkit.mozbuild')
 
 if CONFIG['MOZ_EXTENSIONS']:
     DIRS += ['/extensions']
 
 DIRS += [
     '/%s' % CONFIG['MOZ_BRANDING_DIRECTORY'],
     '/b2g',
-    '/devtools',
 ]

--- a/b2g/graphene/app.mozbuild
+++ b/b2g/graphene/app.mozbuild
@@ -6,13 +6,12 @@
 include('/toolkit/toolkit.mozbuild')
 
 if CONFIG['MOZ_EXTENSIONS']:
     DIRS += ['/extensions']
 
 DIRS += [
     '/%s' % CONFIG['MOZ_BRANDING_DIRECTORY'],
     '/b2g',
-    '/devtools',
 ]
 
 # Add the defaults settings.
 FINAL_TARGET_FILES.defaults += [ 'b2g/graphene/settings.json' ]

--- a/browser/moz.build
+++ b/browser/moz.build
@@ -12,17 +12,16 @@ DIRS += [
     'base',
     'components',
     'experiments',
     'fuel',
     'locales',
     'modules',
     'themes',
     'extensions',
-    '/devtools',
 ]
 
 DIRS += [
     'app',
 ]
 
 if CONFIG['MAKENSISU']:
     DIRS += ['installer/windows']

--- a/devtools/moz.build
+++ b/devtools/moz.build
@@ -1,16 +1,25 @@
 # -*- 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/.
 
+if CONFIG['MOZ_DEVTOOLS'] not in ('all', 'server'):
+    error('Unsupported MOZ_DEVTOOLS value: %s' % (CONFIG['MOZ_DEVTOOLS']))
+
 if CONFIG['MOZ_DEVTOOLS'] == 'all':
     DIRS += [
         'client',
     ]
 
-if CONFIG['MOZ_DEVTOOLS'] in ('all', 'server'):
-    DIRS += [
-        'server',
-        'shared',
-    ]
+DIRS += [
+    'server',
+    'shared',
+]
+
+# /browser uses DIST_SUBDIR.  We opt-in to this treatment when building
+# DevTools for the browser to keep the root omni.ja slim for use by external XUL
+# apps.  Mulet also uses this since it includes /browser.
+if CONFIG['MOZ_BUILD_APP'] in ('browser', 'b2g/dev'):
+    DIST_SUBDIR = 'browser'
+    export('DIST_SUBDIR')

--- a/embedding/ios/app.mozbuild
+++ b/embedding/ios/app.mozbuild
@@ -3,12 +3,8 @@
 # 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('/toolkit/toolkit.mozbuild')
 
 if CONFIG['MOZ_EXTENSIONS']:
     DIRS += ['/extensions']
-
-DIRS += [
-    '/devtools',
-]

--- a/mobile/android/app.mozbuild
+++ b/mobile/android/app.mozbuild
@@ -9,10 +9,9 @@ if CONFIG['ENABLE_TESTS']:
     DIRS += ['/testing/instrumentation']
 
 if CONFIG['MOZ_EXTENSIONS']:
     DIRS += ['/extensions']
 
 DIRS += [
     '/%s' % CONFIG['MOZ_BRANDING_DIRECTORY'],
     '/mobile/android',
-    '/devtools',
 ]

--- a/mobile/android/b2gdroid/app.mozbuild
+++ b/mobile/android/b2gdroid/app.mozbuild
@@ -9,10 +9,9 @@ if CONFIG['ENABLE_TESTS']:
     DIRS += ['/testing/instrumentation']
 
 if CONFIG['MOZ_EXTENSIONS']:
     DIRS += ['/extensions']
 
 DIRS += [
     '/%s' % CONFIG['MOZ_BRANDING_DIRECTORY'],
     '/mobile/android/b2gdroid',
-    '/devtools',
 ]

--- a/toolkit/toolkit.mozbuild
+++ b/toolkit/toolkit.mozbuild
@@ -135,16 +135,17 @@ DIRS += [
     '/security/manager',
     '/toolkit',
 ]
 
 if CONFIG['MOZ_PREF_EXTENSIONS']:
     DIRS += ['/extensions/pref']
 
 DIRS += [
+    '/devtools',
     '/services',
     '/startupcache',
     '/js/ductwork/debugger',
     '/other-licenses/snappy',
 ]
 
 if CONFIG['MOZ_GIO_COMPONENT']:
     DIRS += ['/extensions/gio']

--- a/xulrunner/app.mozbuild
+++ b/xulrunner/app.mozbuild
@@ -5,10 +5,9 @@
 
 include('/toolkit/toolkit.mozbuild')
 
 if CONFIG['MOZ_EXTENSIONS']:
     DIRS += ['/extensions']
 
 DIRS += [
     '/xulrunner',
-    '/devtools',
 ]