javascript event.target not working in mozilla

Answer 1

Pass event to the function:

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function fun(event, userID)
{
    event= event|| window.event;
    var btn = event.target; 
    alert(btn.id);
}

OR

Make sure your event is not undefined

function fun(userID)
{
    var e = event || window.event;
    var btn = e.target; 
    alert(btn.id);
}