--- a/testing/marionette/element.js
+++ b/testing/marionette/element.js
@@ -868,16 +868,18 @@ element.isVisible = function(el, x = und
  * @return {boolean}
  *     True if element is obscured, false otherwise.
  */
 element.isObscured = function(el) {
   let tree = element.getPointerInteractablePaintTree(el);
   return !el.contains(tree[0]);
 };
 
+// TODO(ato): Only used by deprecated action API
+// https://bugzil.la/1354578
 /**
  * Calculate the in-view centre point of the area of the given DOM client
  * rectangle that is inside the viewport.
  *
  * @param {DOMRect} rect
  *     Element off a DOMRect sequence produced by calling |getClientRects|
  *     on a |DOMElement|.
  * @param {nsIDOMWindow} win