f mode refer to z-index

[s890081tonyhsu]

As we know that f mode is used to select the button or the link.
But such website like facebook's notifycations as you see, I can't select the function I want because f-mode of the button behind the notifycation will hide f-mode of the notifycation.

I think if the f-mode can check the z-index of each div, it will fix the problem.

I'm sorry that my english is poor, but I think you can figure out from my picture.