Event to know when a browser is closed

Question

I have a website with mutliple tabs and with multiple menu items with a master page.How to know when the browser/tab is closed.I need to close a thread on browser close.

 

I Haved tried this event

<script type="text/javascript">
window.addEventListener('beforeunload', function (e) {
e.preventDefault();
e.returnValue = '';
});
</script>

This event is getting invoked when i am moving from one tab to other and even from one menu item to other.I want to know only when the the browser/tab is getting closed.