onclick = function (e)的疑惑

<% @ Page Language = " C# "  AutoEventWireup = " true "  CodeFile = " __mouseMoveDrop.aspx.cs "  Inherits = " __mouseMoveDrop "   %>

<! DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd" >

< html  xmlns ="http://www.w3.org/1999/xhtml" >
< head  runat ="server" >
     < title ></ title >

</ head >
< body >
     < form  id ="form1"  runat ="server" >
     < div  id ="tt"  style =" background-color:Gray;height: 59px;" >
    
     </ div >
     </ form >
         < script  type ="text/javascript" >
            document.getElementById( ' tt ' ).onclick  =   function  () {
                alert( ' eeeee ' );
            }

     </ script >
</ body >
</ html >

其实在firefox底下是有onclick 事件的