Textbox issue with chrome and firefox. pls help me out

i am giving some value in textbox1 (take for example vishal). so, when i give tab, it(vishal) should assign in textbox2.

so, i used the following in aspx and java script:

aspx:

onchange="getval()"

javascript

function getval() {

var keyCode = event.keyCode ? event.keyCode : event.which ? event.which : event.charCode;
document.getElementById('<%=textbox2.ClientID %>').value = document.getElementById('<%=textbox1.ClientID %>').value;
}

It works correctly in chrome . but, not working in firefox. pls help me out.