Recover the original HTML or DOM before modification from Javascript

A legacy website uses Javascript to remove certain elements when not compatible with the current browser. Something like:

if (!navigator.javaEnabled())
  document.getElementById('greenscreen').innerHTML = '<p>Not Supported on this browser';

Is there a simple way to either recover the original HTML / DOM (at least of the deleted elements), or to ensure our script runs before this script, or to otherwise find out what was in #greenscreen? We can’t modify the existing Javascript, but need to somehow add new Javascript to parse the #greenscreen HTML and get the info.