diff --git a/b2g/app.mozbuild b/b2g/app.mozbuild
index 716f9ba0c51..4587438d5f5 100644
--- a/b2g/app.mozbuild
+++ b/b2g/app.mozbuild
@@ -12,5 +12,4 @@ if CONFIG['MOZ_EXTENSIONS']:
 DIRS += [
     '/%s' % CONFIG['MOZ_BRANDING_DIRECTORY'],
     '/b2g',
-    '/devtools',
 ]
diff --git a/b2g/graphene/app.mozbuild b/b2g/graphene/app.mozbuild
index c5472265976..0985b613c73 100644
--- a/b2g/graphene/app.mozbuild
+++ b/b2g/graphene/app.mozbuild
@@ -11,7 +11,6 @@ if CONFIG['MOZ_EXTENSIONS']:
 DIRS += [
     '/%s' % CONFIG['MOZ_BRANDING_DIRECTORY'],
     '/b2g',
-    '/devtools',
 ]
 
 # Add the defaults settings.
diff --git a/browser/moz.build b/browser/moz.build
index b7e7c79d8c0..571f5156778 100644
--- a/browser/moz.build
+++ b/browser/moz.build
@@ -17,7 +17,6 @@ DIRS += [
     'modules',
     'themes',
     'extensions',
-    '/devtools',
 ]
 
 DIRS += [
diff --git a/devtools/moz.build b/devtools/moz.build
index 3753ab2cefe..7db6e5c6b8c 100644
--- a/devtools/moz.build
+++ b/devtools/moz.build
@@ -4,13 +4,22 @@
 # 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')
diff --git a/embedding/ios/app.mozbuild b/embedding/ios/app.mozbuild
index d63b2f67e38..efba9e77ff0 100644
--- a/embedding/ios/app.mozbuild
+++ b/embedding/ios/app.mozbuild
@@ -8,7 +8,3 @@ include('/toolkit/toolkit.mozbuild')
 
 if CONFIG['MOZ_EXTENSIONS']:
     DIRS += ['/extensions']
-
-DIRS += [
-    '/devtools',
-]
diff --git a/mobile/android/app.mozbuild b/mobile/android/app.mozbuild
index 102a6a98d1b..b29d15c0774 100644
--- a/mobile/android/app.mozbuild
+++ b/mobile/android/app.mozbuild
@@ -14,5 +14,4 @@ if CONFIG['MOZ_EXTENSIONS']:
 DIRS += [
     '/%s' % CONFIG['MOZ_BRANDING_DIRECTORY'],
     '/mobile/android',
-    '/devtools',
 ]
diff --git a/mobile/android/b2gdroid/app.mozbuild b/mobile/android/b2gdroid/app.mozbuild
index 33e2ccccf19..12d933bda00 100644
--- a/mobile/android/b2gdroid/app.mozbuild
+++ b/mobile/android/b2gdroid/app.mozbuild
@@ -14,5 +14,4 @@ if CONFIG['MOZ_EXTENSIONS']:
 DIRS += [
     '/%s' % CONFIG['MOZ_BRANDING_DIRECTORY'],
     '/mobile/android/b2gdroid',
-    '/devtools',
 ]
diff --git a/toolkit/toolkit.mozbuild b/toolkit/toolkit.mozbuild
index f24fad60680..f3f00be75b1 100644
--- a/toolkit/toolkit.mozbuild
+++ b/toolkit/toolkit.mozbuild
@@ -140,6 +140,7 @@ if CONFIG['MOZ_PREF_EXTENSIONS']:
     DIRS += ['/extensions/pref']
 
 DIRS += [
+    '/devtools',
     '/services',
     '/startupcache',
     '/js/ductwork/debugger',
diff --git a/xulrunner/app.mozbuild b/xulrunner/app.mozbuild
index f040261353b..2902b760778 100644
--- a/xulrunner/app.mozbuild
+++ b/xulrunner/app.mozbuild
@@ -10,5 +10,4 @@ if CONFIG['MOZ_EXTENSIONS']:
 
 DIRS += [
     '/xulrunner',
-    '/devtools',
 ]