--- a/layout/style/test/moz.build
+++ b/layout/style/test/moz.build
@@ -94,8 +94,10 @@ TEST_HARNESS_FILES.testing.mochitest.tes
     '/layout/reftests/svg/as-image/lime100x100.svg',
     '/layout/reftests/svg/as-image/svg-image-visited-1-helper.svg',
     '/layout/reftests/svg/as-image/svg-image-visited-2-helper.svg',
     '/layout/reftests/svg/pseudo-classes-02-ref.svg',
     '/layout/reftests/svg/pseudo-classes-02.svg',
 ]
 
 DEFINES['MOZILLA_INTERNAL_API'] = True
+if CONFIG['MOZ_ENABLE_MASK_AS_SHORTHAND']:
+   HOST_DEFINES['MOZ_ENABLE_MASK_AS_SHORTHAND'] = True

--- a/old-configure.in
+++ b/old-configure.in
@@ -9024,16 +9024,26 @@ else
 fi
 
 if test "$MOZ_WIDGET_TOOLKIT" = "cocoa"; then
     USE_ICU=1
 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
 AC_SUBST(JS_SHARED_LIBRARY)
 
 # Avoid using obsolete NSPR features
 AC_DEFINE(NO_NSPR_10_SUPPORT)