diff --git a/b2g/app/moz.build b/b2g/app/moz.build
index 2534bc5e8c6..5f4eea54f2e 100644
--- a/b2g/app/moz.build
+++ b/b2g/app/moz.build
@@ -74,7 +74,7 @@ if CONFIG['OS_ARCH'] == 'WINNT':
 if CONFIG['GNU_CXX']:
     CXXFLAGS += ['-Wshadow']
 
-JS_PREFERENCE_FILES += [
+JS_PREFERENCE_PP_FILES += [
     'b2g.js',
 ]
 
diff --git a/b2g/dev/app/moz.build b/b2g/dev/app/moz.build
index 50675f87b54..540170626f9 100644
--- a/b2g/dev/app/moz.build
+++ b/b2g/dev/app/moz.build
@@ -5,8 +5,11 @@
 DIST_SUBDIR = 'browser'
 export('DIST_SUBDIR')
 
-JS_PREFERENCE_FILES += [
+JS_PREFERENCE_PP_FILES += [
     '/b2g/app/b2g.js',
+]
+
+JS_PREFERENCE_FILES += [
     '/b2g/dev/app/mulet.js',
 ]
 
diff --git a/browser/app/moz.build b/browser/app/moz.build
index e10ddf093af..e4d9d053200 100644
--- a/browser/app/moz.build
+++ b/browser/app/moz.build
@@ -11,7 +11,7 @@ if CONFIG['OS_ARCH'] == 'WINNT' and CONFIG['MOZ_ASAN']:
 else:
     GeckoProgram(CONFIG['MOZ_APP_NAME'], msvcrt='static')
 
-JS_PREFERENCE_FILES += [
+JS_PREFERENCE_PP_FILES += [
     'profile/firefox.js',
 ]
 
diff --git a/devtools/client/preferences/moz.build b/devtools/client/preferences/moz.build
index b26d73600e6..0cec0a0dbc3 100644
--- a/devtools/client/preferences/moz.build
+++ b/devtools/client/preferences/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/.
 
-JS_PREFERENCE_FILES += [
+JS_PREFERENCE_PP_FILES += [
     'devtools.js',
 ]
diff --git a/devtools/client/webide/moz.build b/devtools/client/webide/moz.build
index 473f6d6eaed..bed6dda019f 100644
--- a/devtools/client/webide/moz.build
+++ b/devtools/client/webide/moz.build
@@ -18,6 +18,6 @@ MOCHITEST_CHROME_MANIFESTS += [
     'test/chrome.ini'
 ]
 
-JS_PREFERENCE_FILES += [
+JS_PREFERENCE_PP_FILES += [
     'webide-prefs.js',
 ]
diff --git a/mobile/android/app/moz.build b/mobile/android/app/moz.build
index 729042d7be8..469a06b979c 100644
--- a/mobile/android/app/moz.build
+++ b/mobile/android/app/moz.build
@@ -13,7 +13,7 @@ for var in ('MOZ_UPDATER', 'MOZ_APP_UA_NAME', 'ANDROID_PACKAGE_NAME'):
 if CONFIG['MOZ_PKG_SPECIAL']:
     DEFINES['MOZ_PKG_SPECIAL'] = CONFIG['MOZ_PKG_SPECIAL']
 
-JS_PREFERENCE_FILES += [
+JS_PREFERENCE_PP_FILES += [
      'mobile.js',
 ]
 
diff --git a/mobile/android/b2gdroid/app/moz.build b/mobile/android/b2gdroid/app/moz.build
index 76332b4e145..7594d58687e 100644
--- a/mobile/android/b2gdroid/app/moz.build
+++ b/mobile/android/b2gdroid/app/moz.build
@@ -33,6 +33,6 @@ if CONFIG['ANDROID_APPCOMPAT_V7_AAR']:
     ANDROID_EXTRA_PACKAGES += ['android.support.v7.appcompat']
     ANDROID_EXTRA_RES_DIRS += ['%' + CONFIG['ANDROID_APPCOMPAT_V7_AAR_RES']]
 
-JS_PREFERENCE_FILES += [
+JS_PREFERENCE_PP_FILES += [
      'b2gdroid.js',
 ]
diff --git a/python/mozbuild/mozbuild/frontend/context.py b/python/mozbuild/mozbuild/frontend/context.py
index 21e3253447a..f9875492dac 100644
--- a/python/mozbuild/mozbuild/frontend/context.py
+++ b/python/mozbuild/mozbuild/frontend/context.py
@@ -1096,6 +1096,10 @@ VARIABLES = {
         Path will be defined for gre or application prefs dir based on what is building.
         """, 'libs'),
 
+    'JS_PREFERENCE_PP_FILES': (StrictOrderingOnAppendList, list,
+        """Like JS_PREFERENCE_FILES, preprocessed..
+        """, 'libs'),
+
     'LIBRARY_DEFINES': (OrderedDict, dict,
         """Dictionary of compiler defines to declare for the entire library.
 
diff --git a/python/mozbuild/mozbuild/frontend/emitter.py b/python/mozbuild/mozbuild/frontend/emitter.py
index 21d0717d62c..e9b648cdd33 100644
--- a/python/mozbuild/mozbuild/frontend/emitter.py
+++ b/python/mozbuild/mozbuild/frontend/emitter.py
@@ -637,7 +637,8 @@ class TreeMetadataEmitter(LoggingMixin):
                     'XPI_NAME.', context)
             yield Resources(context, resources)
 
-        for pref in sorted(context['JS_PREFERENCE_FILES']):
+        for pref in sorted(context['JS_PREFERENCE_FILES'] +
+                           context['JS_PREFERENCE_PP_FILES']):
             yield JsPreferenceFile(context, pref)
 
         self._handle_programs(context)
diff --git a/webapprt/moz.build b/webapprt/moz.build
index d65374649eb..5336c4d1733 100644
--- a/webapprt/moz.build
+++ b/webapprt/moz.build
@@ -50,7 +50,7 @@ DEFINES['MOZ_APP_BASENAME'] = CONFIG['MOZ_APP_BASENAME']
 
 JAR_MANIFESTS += ['jar.mn']
 
-JS_PREFERENCE_FILES += [
+JS_PREFERENCE_PP_FILES += [
     'prefs.js',
 ]
 
diff --git a/xulrunner/app/moz.build b/xulrunner/app/moz.build
index 0195a439906..b08e77165bf 100644
--- a/xulrunner/app/moz.build
+++ b/xulrunner/app/moz.build
@@ -54,7 +54,7 @@ if CONFIG['OS_ARCH'] == 'WINNT':
 
 DISABLE_STL_WRAPPING = True
 
-JS_PREFERENCE_FILES += [
+JS_PREFERENCE_PP_FILES += [
     'xulrunner.js',
 ]