This has been asked before, but I can only find fixes/hacks for deprecated versions of Superfish.
If you shrink the screen, you can see that the nested/child lists are rendered off-screen. Is it possible to fix this shortcoming so that child menus display to the left instead of the right, or recognise the screen edge in some fashion?
The nested ul-elements are positioned with ' position: absolute; ', perhaps you can think of a way to make them work with ' position: relative; '.
But where would you expect them to show up? It would be strange if it suddenly moved to the left side....
Best solutions: On smaller screens, use another kind of menu.