diff --git a/webapprt/Makefile.in b/webapprt/Makefile.in
index 8afcdf1c70c6..c4b3c2bb1788 100644
--- a/webapprt/Makefile.in
+++ b/webapprt/Makefile.in
@@ -9,26 +9,12 @@ VPATH     = @srcdir@
 
 include $(DEPTH)/config/autoconf.mk
 
-DIRS = $(NULL)
-
 # Include config.mk explicitly so we can override FINAL_TARGET.
 include $(topsrcdir)/config/config.mk
 
 # Place webapprt resources in a separate app dir
 DIST_SUBDIR = webapprt
 
-ifneq (,$(filter WINNT,$(OS_ARCH)))
-DIRS += win
-else
-ifeq ($(OS_ARCH),Darwin)
-DIRS += mac
-else
-ifeq ($(MOZ_WIDGET_TOOLKIT),gtk2)
-DIRS += gtk2
-endif # gtk2
-endif # mac
-endif # windows
-
 EXTRA_COMPONENTS := \
   components.manifest \
   CommandLineHandler.js \
@@ -46,10 +32,6 @@ EXTRA_JS_MODULES = \
 PREF_JS_EXPORTS = $(srcdir)/prefs.js \
                   $(NULL)
 
-TEST_DIRS += \
-  test \
-  $(NULL)
-
 include $(topsrcdir)/config/rules.mk
 
 ifdef MOZ_DEBUG
diff --git a/webapprt/gtk2/moz.build b/webapprt/gtk2/moz.build
new file mode 100644
index 000000000000..58ce5e273390
--- /dev/null
+++ b/webapprt/gtk2/moz.build
@@ -0,0 +1,5 @@
+# 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/.
+
diff --git a/webapprt/mac/moz.build b/webapprt/mac/moz.build
new file mode 100644
index 000000000000..58ce5e273390
--- /dev/null
+++ b/webapprt/mac/moz.build
@@ -0,0 +1,5 @@
+# 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/.
+
diff --git a/webapprt/moz.build b/webapprt/moz.build
new file mode 100644
index 000000000000..0c803c3f73b1
--- /dev/null
+++ b/webapprt/moz.build
@@ -0,0 +1,13 @@
+# 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['OS_ARCH'] == 'WINNT':
+    DIRS += ['win']
+elif CONFIG['OS_ARCH'] == 'Darwin':
+    DIRS += ['mac']
+elif CONFIG['MOZ_WIDGET_TOOLKIT'] == 'gtk2':
+    DIRS += ['gtk2']
+
+TEST_DIRS += ['test']
diff --git a/webapprt/test/Makefile.in b/webapprt/test/Makefile.in
index 087c744b24a4..30f6282c1926 100644
--- a/webapprt/test/Makefile.in
+++ b/webapprt/test/Makefile.in
@@ -9,9 +9,4 @@ VPATH     = @srcdir@
 
 include $(DEPTH)/config/autoconf.mk
 
-DIRS += \
-  chrome \
-  content \
-  $(NULL)
-
 include $(topsrcdir)/config/rules.mk
diff --git a/webapprt/test/chrome/moz.build b/webapprt/test/chrome/moz.build
new file mode 100644
index 000000000000..58ce5e273390
--- /dev/null
+++ b/webapprt/test/chrome/moz.build
@@ -0,0 +1,5 @@
+# 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/.
+
diff --git a/webapprt/test/content/moz.build b/webapprt/test/content/moz.build
new file mode 100644
index 000000000000..58ce5e273390
--- /dev/null
+++ b/webapprt/test/content/moz.build
@@ -0,0 +1,5 @@
+# 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/.
+
diff --git a/webapprt/test/moz.build b/webapprt/test/moz.build
new file mode 100644
index 000000000000..ac35ec1447eb
--- /dev/null
+++ b/webapprt/test/moz.build
@@ -0,0 +1,6 @@
+# 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/.
+
+DIRS += ['chrome', 'content']
diff --git a/webapprt/win/moz.build b/webapprt/win/moz.build
new file mode 100644
index 000000000000..58ce5e273390
--- /dev/null
+++ b/webapprt/win/moz.build
@@ -0,0 +1,5 @@
+# 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/.
+