Editor: Revoke old ObjectURLs

editor/js/Menubar.File.js

@@ -488,12 +488,16 @@ function MenubarFile( editor ) {
 	var link = document.createElement( 'a' );
 	function save( blob, filename ) {
 
+		if ( link.href ) {
+
+			URL.revokeObjectURL( link.href );
+
+		}
+
 		link.href = URL.createObjectURL( blob );
 		link.download = filename || 'data.json';
 		link.dispatchEvent( new MouseEvent( 'click' ) );
 
-		// URL.revokeObjectURL( url ); breaks Firefox...
-
 	}
 
 	function saveArrayBuffer( buffer, filename ) {