diff --git a/layout/style/test/moz.build b/layout/style/test/moz.build
index 38ad8af6c2b8..4e06ee597015 100644
--- a/layout/style/test/moz.build
+++ b/layout/style/test/moz.build
@@ -99,3 +99,5 @@ TEST_HARNESS_FILES.testing.mochitest.tests.layout.style.test['css-visited'] += [
 ]
 
 DEFINES['MOZILLA_INTERNAL_API'] = True
+if CONFIG['MOZ_ENABLE_MASK_AS_SHORTHAND']:
+   HOST_DEFINES['MOZ_ENABLE_MASK_AS_SHORTHAND'] = True
diff --git a/old-configure.in b/old-configure.in
index e5cfee9f44ff..0e8aa7e81217 100644
--- a/old-configure.in
+++ b/old-configure.in
@@ -8943,6 +8943,16 @@ fi
 
 MOZ_CONFIG_ICU()
 
+dnl ========================================================
+dnl mask as short hand property
+dnl ========================================================
+dnl Uncommenting the next line would enable mask-as-shorthand feature.
+dnl MOZ_ENABLE_MASK_AS_SHORTHAND=1
+if test "$MOZ_ENABLE_MASK_AS_SHORTHAND"; then
+  AC_DEFINE(MOZ_ENABLE_MASK_AS_SHORTHAND)
+fi
+AC_SUBST(MOZ_ENABLE_MASK_AS_SHORTHAND)
+
 if test -z "$JS_SHARED_LIBRARY"; then
   AC_DEFINE(MOZ_STATIC_JS)
 fi