UserAgent: Mozilla/5.0 (Windows NT 6.2; rv:49.0) Gecko/20100101 Firefox/49.0

Steps to reproduce the problem:
1. Open a child window from parent window using 'window.open' function in parent.

2. In child window, add the following code so that parent window is refreshed/reloaded when child window's 'onUnload' event is triggered either on close or refresh operation.

window.onunload = refreshParent;
function refreshParent() {
  window.opener.location.reload();
}

3. Open child window from parent window and then either close or refresh the child window.

What is the expected behavior?
Expected behavior is that when child window is closed/refreshed, its 'onUnload' event should be triggered and parent window should be refreshed.

What went wrong?
I believe 'onUnload' event has stopped working in the latest version.

Thing worth noting is that it used to work before the upgrade to the latest version and continues working in other browsers such as 'Microsoft IE' and 'Mozilla FF'.

Did this work before? Yes Previous to the upgrade.

Chrome version: 54.0.2840.71 m  Channel: n/a
OS Version: 6.2 (Windows 8)
Flash Version: 

I have outlined the issue in detail with the code and reproduction steps on http://stackoverflow.com/questions/40280974/javascript-onunload-event-not-working-in-latest-version-54-0-2840-71-m-of-go