diff --git a/browser/components/customizableui/moz.build b/browser/components/customizableui/moz.build
index 4c20c05f55f..8d490b611a8 100644
--- a/browser/components/customizableui/moz.build
+++ b/browser/components/customizableui/moz.build
@@ -4,7 +4,7 @@
 # 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/.
 
-PARALLEL_DIRS += [
+DIRS += [
     'content',
 ]
 
diff --git a/browser/components/moz.build b/browser/components/moz.build
index 8b760d7f5ef..30b6612348b 100644
--- a/browser/components/moz.build
+++ b/browser/components/moz.build
@@ -4,7 +4,7 @@
 # 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/.
 
-PARALLEL_DIRS += [
+DIRS += [
     'about',
     'customizableui',
     'dirprovider',
diff --git a/browser/components/preferences/moz.build b/browser/components/preferences/moz.build
index 3bc4ffcb7ac..89b52083a03 100644
--- a/browser/components/preferences/moz.build
+++ b/browser/components/preferences/moz.build
@@ -4,7 +4,7 @@
 # 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/.
 
-PARALLEL_DIRS += ['in-content']
+DIRS += ['in-content']
 
 BROWSER_CHROME_MANIFESTS += [
     'in-content/tests/browser.ini',
diff --git a/browser/devtools/webide/moz.build b/browser/devtools/webide/moz.build
index 5a089c0614e..54103b07d8d 100644
--- a/browser/devtools/webide/moz.build
+++ b/browser/devtools/webide/moz.build
@@ -4,7 +4,7 @@
 # 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/.
 
-PARALLEL_DIRS += [
+DIRS += [
     'content',
     'components',
     'themes',
diff --git a/browser/moz.build b/browser/moz.build
index c84881f136b..bd3ad500e3a 100644
--- a/browser/moz.build
+++ b/browser/moz.build
@@ -6,7 +6,7 @@
 
 CONFIGURE_SUBST_FILES += ['installer/Makefile']
 
-PARALLEL_DIRS += [
+DIRS += [
     'base',
     'components',
     'experiments',
diff --git a/config/external/moz.build b/config/external/moz.build
index b97d6fd87e8..5ac8009a010 100644
--- a/config/external/moz.build
+++ b/config/external/moz.build
@@ -46,4 +46,4 @@ external_dirs += [
     'media/libsoundtouch',
 ]
 
-PARALLEL_DIRS += ['../../' + i for i in external_dirs]
+DIRS += ['../../' + i for i in external_dirs]
diff --git a/config/makefiles/debugmake.mk b/config/makefiles/debugmake.mk
index b038d169f32..70d5b5654a7 100644
--- a/config/makefiles/debugmake.mk
+++ b/config/makefiles/debugmake.mk
@@ -61,7 +61,6 @@ ifneq (,$(filter $(PROGRAM) $(HOST_PROGRAM) $(SIMPLE_PROGRAMS) $(HOST_LIBRARY) $
 	)
 	@echo --------------------------------------------------------------------------------
 endif
-	$(LOOP_OVER_PARALLEL_DIRS)
 	$(LOOP_OVER_DIRS)
 
 showbuild:
diff --git a/config/recurse.mk b/config/recurse.mk
index d858572b6f7..39f034e6397 100644
--- a/config/recurse.mk
+++ b/config/recurse.mk
@@ -181,19 +181,9 @@ libs export tools::
 else
 
 define CREATE_SUBTIER_TRAVERSAL_RULE
-PARALLEL_DIRS_$(1) = $$(addsuffix _$(1),$$(PARALLEL_DIRS))
-
-.PHONY: $(1) $$(PARALLEL_DIRS_$(1))
-
-ifdef PARALLEL_DIRS
-$$(PARALLEL_DIRS_$(1)): %_$(1): %/Makefile
-	+@$$(call SUBMAKE,$(1),$$*)
-endif
+.PHONY: $(1)
 
 $(1):: $$(SUBMAKEFILES)
-ifdef PARALLEL_DIRS
-	+@$(MAKE) $$(PARALLEL_DIRS_$(1))
-endif
 	$$(LOOP_OVER_DIRS)
 
 endef
@@ -232,5 +222,4 @@ endif
 
 recurse:
 	@$(RECURSED_COMMAND)
-	$(LOOP_OVER_PARALLEL_DIRS)
 	$(LOOP_OVER_DIRS)
diff --git a/config/rules.mk b/config/rules.mk
index c56bed030bb..ed7c36f59bb 100644
--- a/config/rules.mk
+++ b/config/rules.mk
@@ -349,12 +349,6 @@ LOOP_OVER_DIRS = \
   $(foreach dir,$(DIRS),$(call SUBMAKE,$@,$(dir)))
 endif
 
-# we only use this for the makefiles target and other stuff that doesn't matter
-ifneq (,$(strip $(PARALLEL_DIRS)))
-LOOP_OVER_PARALLEL_DIRS = \
-  $(foreach dir,$(PARALLEL_DIRS),$(call SUBMAKE,$@,$(dir)))
-endif
-
 #
 # Now we can differentiate between objects used to build a library, and
 # objects used to build an executable in the same directory.
@@ -664,7 +658,7 @@ clean clobber realclean clobber_all distclean::
 		-$(call SUBMAKE,$@,$(dir)))
 else
 clean clobber realclean clobber_all distclean::
-	$(foreach dir,$(PARALLEL_DIRS) $(DIRS),-$(call SUBMAKE,$@,$(dir)))
+	$(foreach dir,$(DIRS),-$(call SUBMAKE,$@,$(dir)))
 endif
 
 distclean::
@@ -1280,7 +1274,6 @@ endif # SDK_BINARY
 
 chrome::
 	$(MAKE) realchrome
-	$(LOOP_OVER_PARALLEL_DIRS)
 	$(LOOP_OVER_DIRS)
 
 $(FINAL_TARGET)/chrome: $(call mkdir_deps,$(FINAL_TARGET)/chrome)
@@ -1621,7 +1614,6 @@ tags: TAGS
 
 TAGS: $(CSRCS) $(CPPSRCS) $(wildcard *.h)
 	-etags $(CSRCS) $(CPPSRCS) $(wildcard *.h)
-	$(LOOP_OVER_PARALLEL_DIRS)
 	$(LOOP_OVER_DIRS)
 
 ifndef INCLUDED_DEBUGMAKE_MK #{
@@ -1637,7 +1629,6 @@ documentation:
 
 ifdef ENABLE_TESTS
 check::
-	$(LOOP_OVER_PARALLEL_DIRS)
 	$(LOOP_OVER_DIRS)
 endif
 
diff --git a/content/base/moz.build b/content/base/moz.build
index 0fd9b4c1d5b..92950f53728 100644
--- a/content/base/moz.build
+++ b/content/base/moz.build
@@ -4,5 +4,5 @@
 # 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/.
 
-PARALLEL_DIRS += ['public', 'src']
+DIRS += ['public', 'src']
 TEST_DIRS += ['test']
diff --git a/content/html/content/moz.build b/content/html/content/moz.build
index 0fd9b4c1d5b..92950f53728 100644
--- a/content/html/content/moz.build
+++ b/content/html/content/moz.build
@@ -4,5 +4,5 @@
 # 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/.
 
-PARALLEL_DIRS += ['public', 'src']
+DIRS += ['public', 'src']
 TEST_DIRS += ['test']
diff --git a/content/html/document/moz.build b/content/html/document/moz.build
index a709e27d8d2..7edd2cd6939 100644
--- a/content/html/document/moz.build
+++ b/content/html/document/moz.build
@@ -4,7 +4,7 @@
 # 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/.
 
-PARALLEL_DIRS += ['public', 'src']
+DIRS += ['public', 'src']
 
 MOCHITEST_MANIFESTS += ['test/mochitest.ini']
 BROWSER_CHROME_MANIFESTS += ['test/browser.ini']
diff --git a/content/html/moz.build b/content/html/moz.build
index 6e423898eeb..4b870635ae5 100644
--- a/content/html/moz.build
+++ b/content/html/moz.build
@@ -4,4 +4,4 @@
 # 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/.
 
-PARALLEL_DIRS += ['content', 'document']
+DIRS += ['content', 'document']
diff --git a/content/media/encoder/moz.build b/content/media/encoder/moz.build
index 9a7527a5b31..7d36784739b 100644
--- a/content/media/encoder/moz.build
+++ b/content/media/encoder/moz.build
@@ -5,7 +5,7 @@
 # file, You can obtain one at http://mozilla.org/MPL/2.0/.
 
 if CONFIG['MOZ_WIDGET_TOOLKIT'] == 'gonk':
-    PARALLEL_DIRS += ['fmp4_muxer']
+    DIRS += ['fmp4_muxer']
 
 EXPORTS += [
     'ContainerWriter.h',
diff --git a/content/media/fmp4/moz.build b/content/media/fmp4/moz.build
index 113224f49e6..bc635b56c87 100644
--- a/content/media/fmp4/moz.build
+++ b/content/media/fmp4/moz.build
@@ -21,7 +21,7 @@ SOURCES += [
 ]
 
 if CONFIG['MOZ_WMF']:
-  PARALLEL_DIRS += [ 'wmf' ];
+  DIRS += [ 'wmf' ];
 
 if CONFIG['MOZ_FFMPEG']:
   EXPORTS += [
@@ -31,7 +31,7 @@ if CONFIG['MOZ_FFMPEG']:
       'ffmpeg/FFmpegLog.cpp',
       'ffmpeg/FFmpegRuntimeLinker.cpp',
   ]
-  PARALLEL_DIRS += [
+  DIRS += [
       'ffmpeg/libav53',
       'ffmpeg/libav54',
       'ffmpeg/libav55',
diff --git a/content/media/mediasource/moz.build b/content/media/mediasource/moz.build
index f88677f4ff0..6dd0f37d811 100644
--- a/content/media/mediasource/moz.build
+++ b/content/media/mediasource/moz.build
@@ -3,7 +3,7 @@
 # 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/.
 
-PARALLEL_DIRS += [
+DIRS += [
     'test'
 ]
 
diff --git a/content/media/moz.build b/content/media/moz.build
index a1605907544..5c2fc1c75f1 100644
--- a/content/media/moz.build
+++ b/content/media/moz.build
@@ -4,7 +4,7 @@
 # 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/.
 
-PARALLEL_DIRS += [
+DIRS += [
   'encoder',
   'gmp',
   'mediasource',
@@ -16,42 +16,42 @@ PARALLEL_DIRS += [
 TEST_DIRS += ['compiledtest']
 
 if CONFIG['MOZ_RAW']:
-    PARALLEL_DIRS += ['raw']
+    DIRS += ['raw']
 
 if CONFIG['MOZ_WAVE']:
-    PARALLEL_DIRS += ['wave']
+    DIRS += ['wave']
 
 if CONFIG['MOZ_WEBM']:
-    PARALLEL_DIRS += ['webm']
+    DIRS += ['webm']
 
 if CONFIG['MOZ_GSTREAMER']:
-    PARALLEL_DIRS += ['gstreamer']
+    DIRS += ['gstreamer']
 
 if CONFIG['MOZ_DIRECTSHOW']:
-    PARALLEL_DIRS += ['directshow']
+    DIRS += ['directshow']
 
 if CONFIG['MOZ_ANDROID_OMX']:
-    PARALLEL_DIRS += ['android']
+    DIRS += ['android']
 
 if CONFIG['MOZ_WMF']:
-    PARALLEL_DIRS += ['wmf']
+    DIRS += ['wmf']
 
 if CONFIG['MOZ_FMP4']:
-    PARALLEL_DIRS += ['fmp4']
+    DIRS += ['fmp4']
 
 if CONFIG['MOZ_APPLEMEDIA']:
-    PARALLEL_DIRS += ['apple']
+    DIRS += ['apple']
 
-PARALLEL_DIRS += ['webrtc']
+DIRS += ['webrtc']
 
 if CONFIG['MOZ_OMX_DECODER']:
-    PARALLEL_DIRS += ['omx']
-    PARALLEL_DIRS += ['omx/mediaresourcemanager']
+    DIRS += ['omx']
+    DIRS += ['omx/mediaresourcemanager']
 
-PARALLEL_DIRS += ['webspeech']
+DIRS += ['webspeech']
 
 if CONFIG['MOZ_EME']:
-    PARALLEL_DIRS += ['eme']
+    DIRS += ['eme']
 
 TEST_DIRS += [
     'test',
diff --git a/content/media/webaudio/moz.build b/content/media/webaudio/moz.build
index 26186329856..6f568aa8034 100644
--- a/content/media/webaudio/moz.build
+++ b/content/media/webaudio/moz.build
@@ -4,7 +4,7 @@
 # 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/.
 
-PARALLEL_DIRS += ['blink', 'test']
+DIRS += ['blink', 'test']
 
 TEST_DIRS += ['compiledtest']
 
diff --git a/content/media/webspeech/moz.build b/content/media/webspeech/moz.build
index c3d9759aa32..85e2277b388 100644
--- a/content/media/webspeech/moz.build
+++ b/content/media/webspeech/moz.build
@@ -3,7 +3,7 @@
 # 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/.
 
-PARALLEL_DIRS = ['synth']
+DIRS = ['synth']
 
 if CONFIG['MOZ_WEBSPEECH']:
-    PARALLEL_DIRS += ['recognition']
+    DIRS += ['recognition']
diff --git a/content/media/webspeech/synth/moz.build b/content/media/webspeech/synth/moz.build
index 991703e2e3d..d297d1c60dc 100644
--- a/content/media/webspeech/synth/moz.build
+++ b/content/media/webspeech/synth/moz.build
@@ -35,7 +35,7 @@ if CONFIG['MOZ_WEBSPEECH']:
     ]
 
     if CONFIG['MOZ_SYNTH_PICO']:
-        PARALLEL_DIRS = ['pico']
+        DIRS = ['pico']
 
 IPDL_SOURCES += [
     'ipc/PSpeechSynthesis.ipdl',
diff --git a/content/moz.build b/content/moz.build
index 4ca12397dc8..86650b90b51 100644
--- a/content/moz.build
+++ b/content/moz.build
@@ -4,7 +4,7 @@
 # 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/.
 
-PARALLEL_DIRS += [
+DIRS += [
     'base',
     'html',
     'media',
diff --git a/content/svg/content/moz.build b/content/svg/content/moz.build
index 7a02ecfc9a3..d7694feea73 100644
--- a/content/svg/content/moz.build
+++ b/content/svg/content/moz.build
@@ -4,6 +4,6 @@
 # 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/.
 
-PARALLEL_DIRS += ['src']
+DIRS += ['src']
 
 MOCHITEST_MANIFESTS += ['test/mochitest.ini']
diff --git a/content/svg/moz.build b/content/svg/moz.build
index 5c7647fc213..dd57669525e 100644
--- a/content/svg/moz.build
+++ b/content/svg/moz.build
@@ -4,4 +4,4 @@
 # 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/.
 
-PARALLEL_DIRS += ['document/src', 'content']
+DIRS += ['document/src', 'content']
diff --git a/content/xul/content/moz.build b/content/xul/content/moz.build
index c3ee957316e..47e64e62391 100644
--- a/content/xul/content/moz.build
+++ b/content/xul/content/moz.build
@@ -4,6 +4,6 @@
 # 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/.
 
-PARALLEL_DIRS += ['public', 'src']
+DIRS += ['public', 'src']
 TEST_DIRS += ['test']
 
diff --git a/content/xul/document/moz.build b/content/xul/document/moz.build
index ac02dca4166..dbc31421c33 100644
--- a/content/xul/document/moz.build
+++ b/content/xul/document/moz.build
@@ -4,6 +4,6 @@
 # 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/.
 
-PARALLEL_DIRS += ['public', 'src']
+DIRS += ['public', 'src']
 DIRS += ['test']
 
diff --git a/content/xul/moz.build b/content/xul/moz.build
index 8d394f849e7..5e677c67407 100644
--- a/content/xul/moz.build
+++ b/content/xul/moz.build
@@ -7,8 +7,8 @@
 # We need to build document even if XUL is disabled, for the nsIController[s]
 # interfaces and implementations.
 # Likewise for content, because of nsXULAtoms.
-PARALLEL_DIRS += ['document', 'content']
+DIRS += ['document', 'content']
 
 if CONFIG['MOZ_XUL']:
-    PARALLEL_DIRS += ['templates']
+    DIRS += ['templates']
 
diff --git a/content/xul/templates/moz.build b/content/xul/templates/moz.build
index 18b88fb7837..a728d0c9e0c 100644
--- a/content/xul/templates/moz.build
+++ b/content/xul/templates/moz.build
@@ -4,6 +4,6 @@
 # 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/.
 
-PARALLEL_DIRS += ['public', 'src']
+DIRS += ['public', 'src']
 
 MOCHITEST_CHROME_MANIFESTS += ['tests/chrome/chrome.ini']
diff --git a/dom/activities/moz.build b/dom/activities/moz.build
index bd55e42906a..c48feb89c78 100644
--- a/dom/activities/moz.build
+++ b/dom/activities/moz.build
@@ -4,6 +4,6 @@
 # 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/.
 
-PARALLEL_DIRS += ['interfaces', 'src']
+DIRS += ['interfaces', 'src']
 
 XPCSHELL_TESTS_MANIFESTS += ['tests/unit/xpcshell.ini']
diff --git a/dom/apps/moz.build b/dom/apps/moz.build
index 84478e5b581..e6eb648904f 100644
--- a/dom/apps/moz.build
+++ b/dom/apps/moz.build
@@ -4,7 +4,7 @@
 # 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/.
 
-PARALLEL_DIRS += ['src']
+DIRS += ['src']
 
 XPCSHELL_TESTS_MANIFESTS += ['tests/unit/xpcshell.ini']
 
diff --git a/dom/cellbroadcast/moz.build b/dom/cellbroadcast/moz.build
index 0f03209577a..665ae0da05f 100644
--- a/dom/cellbroadcast/moz.build
+++ b/dom/cellbroadcast/moz.build
@@ -4,4 +4,4 @@
 # 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/.
 
-PARALLEL_DIRS += ['interfaces', 'src']
+DIRS += ['interfaces', 'src']
diff --git a/dom/downloads/moz.build b/dom/downloads/moz.build
index 8deb9caac78..ee732b7b398 100644
--- a/dom/downloads/moz.build
+++ b/dom/downloads/moz.build
@@ -7,4 +7,4 @@
 if CONFIG["MOZ_B2G"]:
     MOCHITEST_MANIFESTS += ['tests/mochitest.ini']
 
-PARALLEL_DIRS += ['src']
+DIRS += ['src']
diff --git a/dom/icc/moz.build b/dom/icc/moz.build
index 0f03209577a..665ae0da05f 100644
--- a/dom/icc/moz.build
+++ b/dom/icc/moz.build
@@ -4,4 +4,4 @@
 # 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/.
 
-PARALLEL_DIRS += ['interfaces', 'src']
+DIRS += ['interfaces', 'src']
diff --git a/dom/messages/moz.build b/dom/messages/moz.build
index 20e7f4c662b..19d8125a58a 100644
--- a/dom/messages/moz.build
+++ b/dom/messages/moz.build
@@ -4,7 +4,7 @@
 # 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/.
 
-PARALLEL_DIRS += ['interfaces']
+DIRS += ['interfaces']
 
 EXTRA_COMPONENTS += [
     'SystemMessageInternal.js',
diff --git a/dom/mobileconnection/moz.build b/dom/mobileconnection/moz.build
index d9982eec489..be9ec3fed96 100644
--- a/dom/mobileconnection/moz.build
+++ b/dom/mobileconnection/moz.build
@@ -4,6 +4,6 @@
 # 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/.
 
-PARALLEL_DIRS += ['interfaces', 'src']
+DIRS += ['interfaces', 'src']
 
 MOCHITEST_MANIFESTS += ['tests/mochitest/mochitest.ini']
diff --git a/dom/mobileid/moz.build b/dom/mobileid/moz.build
index a6aac9a5c03..3a38f4e856a 100644
--- a/dom/mobileid/moz.build
+++ b/dom/mobileid/moz.build
@@ -4,6 +4,6 @@
 # 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/.
 
-PARALLEL_DIRS += ['interfaces', 'src']
+DIRS += ['interfaces', 'src']
 
 MOCHITEST_MANIFESTS += ['test/mochitest.ini']
diff --git a/dom/moz.build b/dom/moz.build
index 50a93da2f17..042a811b2ba 100644
--- a/dom/moz.build
+++ b/dom/moz.build
@@ -32,9 +32,9 @@ interfaces = [
     'gamepad',
 ]
 
-PARALLEL_DIRS += ['interfaces/' + i for i in interfaces]
+DIRS += ['interfaces/' + i for i in interfaces]
 
-PARALLEL_DIRS += [
+DIRS += [
     'animation',
     'apps',
     'base',
@@ -91,16 +91,16 @@ PARALLEL_DIRS += [
 ]
 
 if CONFIG['OS_ARCH'] == 'WINNT':
-    PARALLEL_DIRS += ['plugins/ipc/hangui']
+    DIRS += ['plugins/ipc/hangui']
 
 if CONFIG['MOZ_WIDGET_TOOLKIT'] == 'gonk':
-    PARALLEL_DIRS += [
+    DIRS += [
         'speakermanager',
         'wifi',
     ]
 
 if CONFIG['MOZ_B2G_RIL']:
-    PARALLEL_DIRS += [
+    DIRS += [
         'icc',
         'cellbroadcast',
         'mobileconnection',
@@ -109,24 +109,24 @@ if CONFIG['MOZ_B2G_RIL']:
     ]
 
 if CONFIG['MOZ_PAY']:
-    PARALLEL_DIRS += ['payment']
+    DIRS += ['payment']
 
 if CONFIG['MOZ_GAMEPAD']:
-    PARALLEL_DIRS += ['gamepad']
+    DIRS += ['gamepad']
 
 if CONFIG['MOZ_NFC']:
-    PARALLEL_DIRS += ['nfc']
+    DIRS += ['nfc']
 
 if CONFIG['MOZ_B2G']:
-    PARALLEL_DIRS += [
+    DIRS += [
         'downloads',
         'mobileid'
     ]
 
 if CONFIG['MOZ_B2G_BT_API_V2']:
-    PARALLEL_DIRS += ['bluetooth2']
+    DIRS += ['bluetooth2']
 else:
-    PARALLEL_DIRS += ['bluetooth']
+    DIRS += ['bluetooth']
 
 TEST_DIRS += [
     'tests',
diff --git a/dom/network/moz.build b/dom/network/moz.build
index 76c3f3f886c..fc7d84378bf 100644
--- a/dom/network/moz.build
+++ b/dom/network/moz.build
@@ -4,7 +4,7 @@
 # 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/.
 
-PARALLEL_DIRS += ['interfaces', 'src']
+DIRS += ['interfaces', 'src']
 
 XPCSHELL_TESTS_MANIFESTS += [
     'tests/unit/xpcshell.ini',
diff --git a/dom/payment/moz.build b/dom/payment/moz.build
index c697d97fc0d..c091dcb5fae 100644
--- a/dom/payment/moz.build
+++ b/dom/payment/moz.build
@@ -4,7 +4,7 @@
 # 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/.
 
-PARALLEL_DIRS += ['interfaces']
+DIRS += ['interfaces']
 
 EXTRA_JS_MODULES += [
     'Payment.jsm',
diff --git a/dom/push/moz.build b/dom/push/moz.build
index b9ae06ce9a3..8755860cb37 100644
--- a/dom/push/moz.build
+++ b/dom/push/moz.build
@@ -3,4 +3,4 @@
 # 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/.
 
-PARALLEL_DIRS += ['src']
+DIRS += ['src']
diff --git a/dom/wappush/moz.build b/dom/wappush/moz.build
index 1f6041d326c..0da5a504dfc 100644
--- a/dom/wappush/moz.build
+++ b/dom/wappush/moz.build
@@ -3,7 +3,7 @@
 # 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/.
 
-PARALLEL_DIRS += ['interfaces', 'src']
+DIRS += ['interfaces', 'src']
 
 if CONFIG['ENABLE_TESTS']:
     XPCSHELL_TESTS_MANIFESTS += ['tests/xpcshell.ini']
diff --git a/dom/xbl/moz.build b/dom/xbl/moz.build
index a87a3e78abc..20b30c32650 100644
--- a/dom/xbl/moz.build
+++ b/dom/xbl/moz.build
@@ -4,7 +4,7 @@
 # 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/.
 
-PARALLEL_DIRS += ['builtin']
+DIRS += ['builtin']
 
 EXPORTS += [
     'nsBindingManager.h',
diff --git a/dom/xml/moz.build b/dom/xml/moz.build
index 4630ddcf2cb..3f71a6baa50 100644
--- a/dom/xml/moz.build
+++ b/dom/xml/moz.build
@@ -4,7 +4,7 @@
 # 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/.
 
-PARALLEL_DIRS += ['resources']
+DIRS += ['resources']
 
 TEST_DIRS += ['test']
 
diff --git a/dom/xslt/moz.build b/dom/xslt/moz.build
index 76d70047109..b49d789f1fd 100644
--- a/dom/xslt/moz.build
+++ b/dom/xslt/moz.build
@@ -20,7 +20,7 @@ EXPORTS += [
     'nsIDocumentTransformer.h',
 ]
 
-PARALLEL_DIRS += [
+DIRS += [
     'base',
     'xml',
     'xpath',
diff --git a/editor/libeditor/moz.build b/editor/libeditor/moz.build
index 09eb8acb04c..16c381a80cc 100644
--- a/editor/libeditor/moz.build
+++ b/editor/libeditor/moz.build
@@ -4,4 +4,4 @@
 # 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/.
 
-PARALLEL_DIRS += ['base', 'text', 'html']
+DIRS += ['base', 'text', 'html']
diff --git a/editor/moz.build b/editor/moz.build
index 59834f24586..b2b1ebf6b6e 100644
--- a/editor/moz.build
+++ b/editor/moz.build
@@ -4,7 +4,7 @@
 # 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/.
 
-PARALLEL_DIRS += [
+DIRS += [
     'txtsvc',
     'libeditor',
     'txmgr',
diff --git a/extensions/moz.build b/extensions/moz.build
index 9a91825ed65..a719535ead5 100644
--- a/extensions/moz.build
+++ b/extensions/moz.build
@@ -4,4 +4,4 @@
 # 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/.
 
-PARALLEL_DIRS += CONFIG['MOZ_EXTENSIONS'].split()
+DIRS += CONFIG['MOZ_EXTENSIONS'].split()
diff --git a/image/moz.build b/image/moz.build
index 1fc9e22e090..2c613f196d8 100644
--- a/image/moz.build
+++ b/image/moz.build
@@ -4,7 +4,7 @@
 # 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/.
 
-PARALLEL_DIRS += ['public', 'src', 'decoders', 'encoders']
+DIRS += ['public', 'src', 'decoders', 'encoders']
 DIRS += ['build']
 TEST_DIRS += ['test']
 
diff --git a/intl/moz.build b/intl/moz.build
index 9eb45c42e32..2ff8d7069f0 100644
--- a/intl/moz.build
+++ b/intl/moz.build
@@ -4,7 +4,7 @@
 # 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/.
 
-PARALLEL_DIRS += [
+DIRS += [
     'hyphenation',
     'locale',
     'locales',
diff --git a/layout/inspector/moz.build b/layout/inspector/moz.build
index f18b6a8e15e..31fec7576bc 100644
--- a/layout/inspector/moz.build
+++ b/layout/inspector/moz.build
@@ -49,7 +49,7 @@ LOCAL_INCLUDES += [
 ]
 
 if CONFIG['ENABLE_TESTS']:
-    PARALLEL_DIRS += [
+    DIRS += [
         'tests',
         'tests/chrome',
     ]
diff --git a/layout/mathml/moz.build b/layout/mathml/moz.build
index 19ddb5adf71..44d046c8a8e 100644
--- a/layout/mathml/moz.build
+++ b/layout/mathml/moz.build
@@ -47,7 +47,7 @@ LOCAL_INCLUDES += [
 ]
 
 if CONFIG['ENABLE_TESTS']:
-    PARALLEL_DIRS += [
+    DIRS += [
         'tests',
     ]
 
diff --git a/layout/moz.build b/layout/moz.build
index 42209e693da..68c577dcee5 100644
--- a/layout/moz.build
+++ b/layout/moz.build
@@ -4,7 +4,7 @@
 # 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/.
 
-PARALLEL_DIRS += [
+DIRS += [
     'style',
     'base',
     'generic',
@@ -19,7 +19,7 @@ PARALLEL_DIRS += [
 ]
 
 if CONFIG['NS_PRINTING']:
-    PARALLEL_DIRS += ['printing']
+    DIRS += ['printing']
 
 TEST_DIRS += [
     'tools/reftest',
diff --git a/layout/xul/moz.build b/layout/xul/moz.build
index 451857dfae3..d61201065de 100644
--- a/layout/xul/moz.build
+++ b/layout/xul/moz.build
@@ -75,12 +75,12 @@ if CONFIG['MOZ_XUL']:
     ]
 
 if CONFIG['ENABLE_TESTS']:
-    PARALLEL_DIRS += [
+    DIRS += [
         'test',
     ]
 
 if CONFIG['MOZ_XUL']:
-    PARALLEL_DIRS += ['tree', 'grid']
+    DIRS += ['tree', 'grid']
 
 FAIL_ON_WARNINGS = True
 
diff --git a/mobile/android/moz.build b/mobile/android/moz.build
index 5fe56da0ed4..3dd9ae501c4 100644
--- a/mobile/android/moz.build
+++ b/mobile/android/moz.build
@@ -25,7 +25,7 @@ if not CONFIG['MOZ_ANDROID_MLS_STUMBLER']:
     DIRS.remove('stumbler')
 
 if not CONFIG['LIBXUL_SDK']:
-    PARALLEL_DIRS += ['../../xulrunner/tools/redit']
+    DIRS += ['../../xulrunner/tools/redit']
 
 TEST_DIRS += [
     'tests',
diff --git a/netwerk/moz.build b/netwerk/moz.build
index e817b4ae979..a5e732bcd47 100644
--- a/netwerk/moz.build
+++ b/netwerk/moz.build
@@ -4,7 +4,7 @@
 # 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/.
 
-PARALLEL_DIRS += [
+DIRS += [
     'base',
     'cookie',
     'dns',
@@ -19,15 +19,15 @@ PARALLEL_DIRS += [
 ]
 
 if CONFIG['MOZ_SRTP']:
-    PARALLEL_DIRS += ['srtp/src']
+    DIRS += ['srtp/src']
 
 if CONFIG['MOZ_SCTP']:
-    PARALLEL_DIRS += ['sctp/src', 'sctp/datachannel']
+    DIRS += ['sctp/src', 'sctp/datachannel']
 
 if CONFIG['NECKO_WIFI']:
-    PARALLEL_DIRS += ['wifi']
+    DIRS += ['wifi']
 
-PARALLEL_DIRS += ['locales']
+DIRS += ['locales']
 
 DIRS += ['build']
 TEST_DIRS += ['test']
diff --git a/netwerk/protocol/moz.build b/netwerk/protocol/moz.build
index 68539cb3bc6..7b4ffe3a959 100644
--- a/netwerk/protocol/moz.build
+++ b/netwerk/protocol/moz.build
@@ -4,4 +4,4 @@
 # 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/.
 
-PARALLEL_DIRS += sorted(CONFIG['NECKO_PROTOCOLS'])
+DIRS += sorted(CONFIG['NECKO_PROTOCOLS'])
diff --git a/python/mozbuild/mozbuild/backend/recursivemake.py b/python/mozbuild/mozbuild/backend/recursivemake.py
index c2f0cd6ff5c..e2794c6275d 100644
--- a/python/mozbuild/mozbuild/backend/recursivemake.py
+++ b/python/mozbuild/mozbuild/backend/recursivemake.py
@@ -530,7 +530,7 @@ class RecursiveMakeBackend(CommonBackend):
 
         # Because of bug 925236 and possible other unknown race conditions,
         # don't parallelize the tools tier. There aren't many directories for
-        # this tier anyways, and none of them are under a PARALLEL_DIRS.
+        # this tier anyways.
         def tools_filter(current, subdirs):
             if current not in self._no_skip['tools'] \
                     or current.startswith('subtiers/'):
@@ -848,11 +848,6 @@ class RecursiveMakeBackend(CommonBackend):
             fh.write('DIRS := %s\n' % ' '.join(obj.dirs))
             self._traversal.add(backend_file.relobjdir, dirs=relativize(obj.dirs))
 
-        if obj.parallel_dirs:
-            fh.write('PARALLEL_DIRS := %s\n' % ' '.join(obj.parallel_dirs))
-            self._traversal.add(backend_file.relobjdir,
-                                parallel=relativize(obj.parallel_dirs))
-
         if obj.test_dirs:
             fh.write('TEST_DIRS := %s\n' % ' '.join(obj.test_dirs))
             if self.environment.substs.get('ENABLE_TESTS', False):
diff --git a/python/mozbuild/mozbuild/frontend/data.py b/python/mozbuild/mozbuild/frontend/data.py
index 7dd8444a01c..b75fbe75992 100644
--- a/python/mozbuild/mozbuild/frontend/data.py
+++ b/python/mozbuild/mozbuild/frontend/data.py
@@ -102,7 +102,6 @@ class DirectoryTraversal(SandboxDerived):
     """
     __slots__ = (
         'dirs',
-        'parallel_dirs',
         'test_dirs',
         'tier_dirs',
         'tier_static_dirs',
@@ -112,7 +111,6 @@ class DirectoryTraversal(SandboxDerived):
         SandboxDerived.__init__(self, sandbox)
 
         self.dirs = []
-        self.parallel_dirs = []
         self.test_dirs = []
         self.tier_dirs = OrderedDict()
         self.tier_static_dirs = OrderedDict()
diff --git a/python/mozbuild/mozbuild/frontend/emitter.py b/python/mozbuild/mozbuild/frontend/emitter.py
index 517513156de..6c1a29ab5a9 100644
--- a/python/mozbuild/mozbuild/frontend/emitter.py
+++ b/python/mozbuild/mozbuild/frontend/emitter.py
@@ -934,7 +934,6 @@ class TreeMetadataEmitter(LoggingMixin):
     def _emit_directory_traversal_from_sandbox(self, sandbox):
         o = DirectoryTraversal(sandbox)
         o.dirs = sandbox.get('DIRS', [])
-        o.parallel_dirs = sandbox.get('PARALLEL_DIRS', [])
         o.test_dirs = sandbox.get('TEST_DIRS', [])
         o.affected_tiers = sandbox.get_affected_tiers()
 
diff --git a/python/mozbuild/mozbuild/frontend/reader.py b/python/mozbuild/mozbuild/frontend/reader.py
index 9963fe3c77a..d6708c1d3f2 100644
--- a/python/mozbuild/mozbuild/frontend/reader.py
+++ b/python/mozbuild/mozbuild/frontend/reader.py
@@ -800,7 +800,7 @@ class BuildReader(object):
             self._sandbox_post_eval_cb(sandbox)
 
         # We first collect directories populated in variables.
-        dir_vars = ['DIRS', 'PARALLEL_DIRS']
+        dir_vars = ['DIRS']
 
         if sandbox.config.substs.get('ENABLE_TESTS', False) == '1':
             dir_vars.append('TEST_DIRS')
@@ -839,12 +839,6 @@ class BuildReader(object):
                 gyp_sandbox.update(gyp_dir.sandbox_vars)
                 gyp_sandboxes.append(gyp_sandbox)
 
-        # Add the gyp subdirectories to DIRS. We don't care about trying to
-        # place some of them in PARALLEL_DIRS because they're only going to be
-        # relevant for the compile and libs tiers. The compile tier is already
-        # parallelized, and the libs tier is always serialized, and will remain
-        # so until the library linking operations are moved out of it, at which
-        # point PARALLEL_DIRS will be irrelevant anyways.
         for gyp_sandbox in gyp_sandboxes:
             if self._sandbox_post_eval_cb:
                 self._sandbox_post_eval_cb(gyp_sandbox)
diff --git a/python/mozbuild/mozbuild/frontend/sandbox_symbols.py b/python/mozbuild/mozbuild/frontend/sandbox_symbols.py
index 93b277012a7..bd8db61c84b 100644
--- a/python/mozbuild/mozbuild/frontend/sandbox_symbols.py
+++ b/python/mozbuild/mozbuild/frontend/sandbox_symbols.py
@@ -280,15 +280,6 @@ VARIABLES = {
         Implies FORCE_SHARED_LIB.
         """, None),
 
-    'PARALLEL_DIRS': (list, list,
-        """A parallel version of ``DIRS``.
-
-        Ideally this variable does not exist. It is provided so a transition
-        from recursive makefiles can be made. Once the build system has been
-        converted to not use Makefile's for the build frontend, this will
-        likely go away.
-        """, None),
-
     'PYTHON_UNIT_TESTS': (StrictOrderingOnAppendList, list,
         """A list of python unit tests.
         """, None),
@@ -930,9 +921,9 @@ FUNCTIONS = {
         """Make the specified variable available to all child directories.
 
         The variable specified by the argument string is added to the
-        environment of all directories specified in the DIRS, PARALLEL_DIRS,
-        and TEST_DIRS variables. If those directories themselves have child
-        directories, the variable will be exported to all of them.
+        environment of all directories specified in the DIRS and TEST_DIRS
+        variables. If those directories themselves have child directories,
+        the variable will be exported to all of them.
 
         The value used for the variable is the final value at the end of the
         moz.build file, so it is possible (but not recommended style) to place
@@ -1034,4 +1025,5 @@ SPECIAL_VARIABLES = {
 DEPRECATION_HINTS = {
     'TOOL_DIRS': 'Please use the DIRS variable instead.',
     'TEST_TOOL_DIRS': 'Please use the TEST_DIRS variable instead.',
+    'PARALLEL_DIRS': 'Please use the DIRS variable instead.',
 }
diff --git a/python/mozbuild/mozbuild/test/backend/data/stub0/moz.build b/python/mozbuild/mozbuild/test/backend/data/stub0/moz.build
index 18553bcade7..e7abb0e129f 100644
--- a/python/mozbuild/mozbuild/test/backend/data/stub0/moz.build
+++ b/python/mozbuild/mozbuild/test/backend/data/stub0/moz.build
@@ -3,5 +3,5 @@
 # http://creativecommons.org/publicdomain/zero/1.0/
 
 DIRS += ['dir1']
-PARALLEL_DIRS += ['dir2']
+DIRS += ['dir2']
 TEST_DIRS += ['dir3']
diff --git a/python/mozbuild/mozbuild/test/backend/test_recursivemake.py b/python/mozbuild/mozbuild/test/backend/test_recursivemake.py
index 603a19f2e73..30cc917c079 100644
--- a/python/mozbuild/mozbuild/test/backend/test_recursivemake.py
+++ b/python/mozbuild/mozbuild/test/backend/test_recursivemake.py
@@ -212,8 +212,7 @@ class TestRecursiveMakeBackend(BackendTester):
 
         lines = [l.strip() for l in open(p, 'rt').readlines()[2:]]
         self.assertEqual(lines, [
-            'DIRS := dir1',
-            'PARALLEL_DIRS := dir2',
+            'DIRS := dir1 dir2',
             'TEST_DIRS := dir3',
         ])
 
diff --git a/python/mozbuild/mozbuild/test/frontend/data/traversal-all-vars/moz.build b/python/mozbuild/mozbuild/test/frontend/data/traversal-all-vars/moz.build
index d4103a74c48..f2bcf1fd8dd 100644
--- a/python/mozbuild/mozbuild/test/frontend/data/traversal-all-vars/moz.build
+++ b/python/mozbuild/mozbuild/test/frontend/data/traversal-all-vars/moz.build
@@ -3,5 +3,4 @@
 # http://creativecommons.org/publicdomain/zero/1.0/
 
 DIRS += ['regular']
-PARALLEL_DIRS = ['parallel']
 TEST_DIRS = ['test']
diff --git a/python/mozbuild/mozbuild/test/frontend/test_emitter.py b/python/mozbuild/mozbuild/test/frontend/test_emitter.py
index fda829136c0..ba8e9097899 100644
--- a/python/mozbuild/mozbuild/test/frontend/test_emitter.py
+++ b/python/mozbuild/mozbuild/test/frontend/test_emitter.py
@@ -87,7 +87,6 @@ class TestEmitterBasic(unittest.TestCase):
 
         for o in objs:
             self.assertIsInstance(o, DirectoryTraversal)
-            self.assertEqual(o.parallel_dirs, [])
             self.assertEqual(o.test_dirs, [])
             self.assertEqual(len(o.tier_dirs), 0)
             self.assertEqual(len(o.tier_static_dirs), 0)
@@ -103,20 +102,19 @@ class TestEmitterBasic(unittest.TestCase):
     def test_traversal_all_vars(self):
         reader = self.reader('traversal-all-vars')
         objs = self.read_topsrcdir(reader, filter_common=False)
-        self.assertEqual(len(objs), 4)
+        self.assertEqual(len(objs), 3)
 
         for o in objs:
             self.assertIsInstance(o, DirectoryTraversal)
 
         reldirs = set([o.relativedir for o in objs])
-        self.assertEqual(reldirs, set(['', 'parallel', 'regular', 'test']))
+        self.assertEqual(reldirs, set(['', 'regular', 'test']))
 
         for o in objs:
             reldir = o.relativedir
 
             if reldir == '':
                 self.assertEqual(o.dirs, ['regular'])
-                self.assertEqual(o.parallel_dirs, ['parallel'])
                 self.assertEqual(o.test_dirs, ['test'])
 
     def test_tier_simple(self):
diff --git a/python/mozbuild/mozbuild/test/frontend/test_reader.py b/python/mozbuild/mozbuild/test/frontend/test_reader.py
index 68f89af0582..827f0047b0c 100644
--- a/python/mozbuild/mozbuild/test/frontend/test_reader.py
+++ b/python/mozbuild/mozbuild/test/frontend/test_reader.py
@@ -66,7 +66,7 @@ class TestBuildReader(unittest.TestCase):
         reader = self.reader('traversal-all-vars', enable_tests=True)
 
         sandboxes = list(reader.read_topsrcdir())
-        self.assertEqual(len(sandboxes), 4)
+        self.assertEqual(len(sandboxes), 3)
 
     def test_tiers_traversal(self):
         reader = self.reader('traversal-tier-simple')
diff --git a/services/fxaccounts/moz.build b/services/fxaccounts/moz.build
index f95971425a6..141d23866da 100644
--- a/services/fxaccounts/moz.build
+++ b/services/fxaccounts/moz.build
@@ -4,7 +4,7 @@
 # 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/.
 
-PARALLEL_DIRS += ['interfaces']
+DIRS += ['interfaces']
 
 TEST_DIRS += ['tests']
 
diff --git a/services/mobileid/moz.build b/services/mobileid/moz.build
index e42099d9f24..4c71d8be38b 100644
--- a/services/mobileid/moz.build
+++ b/services/mobileid/moz.build
@@ -4,7 +4,7 @@
 # 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/.
 
-PARALLEL_DIRS += ['interfaces']
+DIRS += ['interfaces']
 
 TEST_DIRS += ['tests']
 
diff --git a/services/moz.build b/services/moz.build
index e75e0914a7a..c394c0d9779 100644
--- a/services/moz.build
+++ b/services/moz.build
@@ -4,7 +4,7 @@
 # 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/.
 
-PARALLEL_DIRS += [
+DIRS += [
     'common',
     'crypto',
     'fxaccounts',
@@ -14,18 +14,18 @@ if CONFIG['MOZ_WIDGET_TOOLKIT'] != 'android':
     # MOZ_SERVICES_HEALTHREPORT and therefore MOZ_DATA_REPORTING are
     # defined on Android, but these features are implemented using Java.
     if CONFIG['MOZ_SERVICES_HEALTHREPORT']:
-        PARALLEL_DIRS += ['healthreport']
+        DIRS += ['healthreport']
 
     if CONFIG['MOZ_DATA_REPORTING']:
-        PARALLEL_DIRS += ['datareporting']
+        DIRS += ['datareporting']
 
 if CONFIG['MOZ_SERVICES_METRICS']:
-    PARALLEL_DIRS += ['metrics']
+    DIRS += ['metrics']
 
 if CONFIG['MOZ_SERVICES_SYNC']:
-    PARALLEL_DIRS += ['sync']
+    DIRS += ['sync']
 
 if CONFIG['MOZ_B2G']:
-    PARALLEL_DIRS += ['mobileid']
+    DIRS += ['mobileid']
 
 SPHINX_TREES['services'] = 'docs'
diff --git a/testing/mochitest/tests/moz.build b/testing/mochitest/tests/moz.build
index 8f56428b25e..130fa8a98c1 100644
--- a/testing/mochitest/tests/moz.build
+++ b/testing/mochitest/tests/moz.build
@@ -4,7 +4,7 @@
 # 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/.
 
-PARALLEL_DIRS += [
+DIRS += [
     'SimpleTest',
     'browser',
 ]
diff --git a/toolkit/components/moz.build b/toolkit/components/moz.build
index 7efc71eaa2c..cdd66b90f6a 100644
--- a/toolkit/components/moz.build
+++ b/toolkit/components/moz.build
@@ -6,9 +6,9 @@
 
 # These component dirs are built for all apps (including suite)
 if CONFIG['MOZ_ENABLE_XREMOTE']:
-    PARALLEL_DIRS += ['remote']
+    DIRS += ['remote']
 
-PARALLEL_DIRS += [
+DIRS += [
     'aboutcache',
     'aboutmemory',
     'addoncompat',
@@ -52,34 +52,34 @@ PARALLEL_DIRS += [
 ]
 
 if CONFIG['MOZ_CRASHREPORTER']:
-    PARALLEL_DIRS += ['crashes']
+    DIRS += ['crashes']
 
 if CONFIG['MOZ_SOCIAL']:
-    PARALLEL_DIRS += ['social']
+    DIRS += ['social']
 
 if CONFIG['BUILD_CTYPES']:
-    PARALLEL_DIRS += ['ctypes']
+    DIRS += ['ctypes']
 
 if CONFIG['MOZ_FEEDS']:
-    PARALLEL_DIRS += ['feeds']
+    DIRS += ['feeds']
 
 if CONFIG['MOZ_HELP_VIEWER']:
-    PARALLEL_DIRS += ['help']
+    DIRS += ['help']
 
 if CONFIG['NS_PRINTING']:
-    PARALLEL_DIRS += ['printing']
+    DIRS += ['printing']
 
 if CONFIG['MOZ_XUL']:
-    PARALLEL_DIRS += ['autocomplete', 'satchel']
+    DIRS += ['autocomplete', 'satchel']
 
 if CONFIG['MOZ_TOOLKIT_SEARCH']:
-    PARALLEL_DIRS += ['search']
+    DIRS += ['search']
 
 if CONFIG['MOZ_URL_CLASSIFIER']:
-    PARALLEL_DIRS += ['url-classifier']
+    DIRS += ['url-classifier']
 
 if CONFIG['MOZ_CAPTIVEDETECT']:
-    PARALLEL_DIRS += ['captivedetect']
+    DIRS += ['captivedetect']
 
 DIRS += ['build']
 
diff --git a/toolkit/components/promiseworker/moz.build b/toolkit/components/promiseworker/moz.build
index c1e362f45a2..4d342f44c2c 100644
--- a/toolkit/components/promiseworker/moz.build
+++ b/toolkit/components/promiseworker/moz.build
@@ -4,7 +4,7 @@
 # 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/.
 
-PARALLEL_DIRS += [
+DIRS += [
     'worker'
 ]
 
diff --git a/toolkit/devtools/moz.build b/toolkit/devtools/moz.build
index 97843dc7c9d..f982eb2a467 100644
--- a/toolkit/devtools/moz.build
+++ b/toolkit/devtools/moz.build
@@ -4,7 +4,7 @@
 # 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/.
 
-PARALLEL_DIRS += [
+DIRS += [
     'server',
     'client',
     'gcli',
diff --git a/toolkit/devtools/qrcode/moz.build b/toolkit/devtools/qrcode/moz.build
index 1e87590c1d8..7651e14c09f 100644
--- a/toolkit/devtools/qrcode/moz.build
+++ b/toolkit/devtools/qrcode/moz.build
@@ -4,7 +4,7 @@
 # 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/.
 
-PARALLEL_DIRS += [
+DIRS += [
     'decoder',
     'encoder'
 ]
diff --git a/toolkit/moz.build b/toolkit/moz.build
index 5847ff914e7..3784ce8f641 100644
--- a/toolkit/moz.build
+++ b/toolkit/moz.build
@@ -4,7 +4,7 @@
 # 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/.
 
-PARALLEL_DIRS += [
+DIRS += [
     'components',
     'content',
     'devtools',
@@ -31,24 +31,24 @@ if CONFIG['MOZ_MAINTENANCE_SERVICE']:
 DIRS += ['xre']
 
 if CONFIG['MOZ_WIDGET_TOOLKIT'] in ('gtk2', 'gtk3', 'qt'):
-    PARALLEL_DIRS += ['system/unixproxy']
+    DIRS += ['system/unixproxy']
 elif CONFIG['MOZ_WIDGET_TOOLKIT'] == 'cocoa':
-    PARALLEL_DIRS += ['system/osxproxy']
+    DIRS += ['system/osxproxy']
 elif CONFIG['MOZ_WIDGET_TOOLKIT'] == 'windows':
-    PARALLEL_DIRS += ['system/windowsproxy']
+    DIRS += ['system/windowsproxy']
 elif CONFIG['MOZ_WIDGET_TOOLKIT'] == 'android':
-    PARALLEL_DIRS += ['system/androidproxy']
+    DIRS += ['system/androidproxy']
 
 if CONFIG['MOZ_CRASHREPORTER']:
-    PARALLEL_DIRS += ['crashreporter']
+    DIRS += ['crashreporter']
 elif CONFIG['MOZ_ENABLE_PROFILER_SPS']:
     # Profiler requires some crashreporter code,
     # so build it even if crashreporter is disabled.
-    PARALLEL_DIRS += [
+    DIRS += [
     'crashreporter/google-breakpad/src/common',
     'crashreporter/google-breakpad/src/processor',
     ]
     if CONFIG['OS_ARCH'] == 'Darwin':
-        PARALLEL_DIRS += ['crashreporter/google-breakpad/src/common/mac']
+        DIRS += ['crashreporter/google-breakpad/src/common/mac']
     elif CONFIG['OS_ARCH'] == 'Linux':
-        PARALLEL_DIRS += ['crashreporter/google-breakpad/src/common/linux']
+        DIRS += ['crashreporter/google-breakpad/src/common/linux']
diff --git a/uriloader/moz.build b/uriloader/moz.build
index 476bb00ad5e..ee90e2f37f9 100644
--- a/uriloader/moz.build
+++ b/uriloader/moz.build
@@ -4,7 +4,7 @@
 # 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/.
 
-PARALLEL_DIRS += [
+DIRS += [
     'base',
     'exthandler',
     'prefetch',
diff --git a/widget/shared/moz.build b/widget/shared/moz.build
index 35980fb14ef..b72e7fbc710 100644
--- a/widget/shared/moz.build
+++ b/widget/shared/moz.build
@@ -5,7 +5,7 @@
 # file, You can obtain one at http://mozilla.org/MPL/2.0/.
 
 if CONFIG['MOZ_X11']:
-    PARALLEL_DIRS += ['x11']
+    DIRS += ['x11']
 
 UNIFIED_SOURCES += [
     'nsShmImage.cpp',
diff --git a/xpcom/moz.build b/xpcom/moz.build
index 09111fb4bc6..0f60e376370 100644
--- a/xpcom/moz.build
+++ b/xpcom/moz.build
@@ -4,7 +4,7 @@
 # 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/.
 
-PARALLEL_DIRS += [
+DIRS += [
     'idl-parser',
 ]
 
diff --git a/xulrunner/moz.build b/xulrunner/moz.build
index 10dc0403292..71c24db607c 100644
--- a/xulrunner/moz.build
+++ b/xulrunner/moz.build
@@ -6,7 +6,7 @@
 
 CONFIGURE_SUBST_FILES += ['installer/Makefile']
 
-PARALLEL_DIRS += [
+DIRS += [
     'app',
     'stub',
     'examples',
@@ -16,4 +16,4 @@ if CONFIG['MAKENSISU']:
     DIRS += ['installer/windows']
 
 if CONFIG['OS_ARCH'] == 'WINNT':
-    PARALLEL_DIRS += ['tools/redit']
+    DIRS += ['tools/redit']