Bug 1568083 - Servo doesn't still support backdrop-filter.

This is a previous build fix that I forgot to sync to Gecko.

servo/components/style/properties/longhands/effects.mako.rs

@@ -68,6 +68,7 @@ ${helpers.predefined_type(
     flags="CREATES_STACKING_CONTEXT FIXPOS_CB",
     gecko_pref="layout.css.backdrop-filter.enabled",
     spec="https://drafts.fxtf.org/filter-effects-2/#propdef-backdrop-filter",
+    products="gecko",
 )}
 
 ${helpers.single_keyword(