diff --git a/components/style/properties/longhands/ui.mako.rs b/components/style/properties/longhands/ui.mako.rs
index 1dfdfcc1a73..400eaedf577 100644
--- a/components/style/properties/longhands/ui.mako.rs
+++ b/components/style/properties/longhands/ui.mako.rs
@@ -53,7 +53,7 @@ ${helpers.single_keyword(
 
 ${helpers.single_keyword(
     "-moz-window-shadow",
-    "default none menu tooltip sheet",
+    "default none menu tooltip sheet cliprounded",
     engines="gecko",
     gecko_ffi_name="mWindowShadow",
     gecko_enum_prefix="StyleWindowShadow",