onbeforeunload works on firefox 44.0.2, with little trick

ff not support onbeforeunload so i did little trick, but for that user needs to click on window at least once.. and it is 90% chances where user click window of browser,

by worse pune

HTML

<body>
<a class="hide javavoid" href="javascript:void(0)">asdf
            </a>
            <p>welcome click anywhere then click on back button or refresh page</p>
</body>

CSS

.hide{display:none;}

JavaScript

$(window).on('beforeunload',function()
    {
    	return "Are you sure you want to exit this page?";
    })
    $(window).one('click',function(){
        alert('hi');
        $('.javavoid').trigger('click');
    })