diff --git a/layout/style/nsCSSProps.cpp b/layout/style/nsCSSProps.cpp
index 6811fe46a43..9bc6e60c05d 100644
--- a/layout/style/nsCSSProps.cpp
+++ b/layout/style/nsCSSProps.cpp
@@ -144,7 +144,6 @@ struct CSSPropertyAlias {
 };
 
 static const CSSPropertyAlias gAliases[] = {
-  { "-moz-opacity", eCSSProperty_opacity },
   { "-moz-outline", eCSSProperty_outline },
   { "-moz-outline-color", eCSSProperty_outline_color },
   { "-moz-outline-style", eCSSProperty_outline_style },