Preavent Copy Paste

hi to all

i want to stop paste in my webpage's textbox
<script type="text/javascript" >

var sSave = "";
function fnBeforeCut() {
event.returnValue = false;
}

function fnCut(id) {
event.returnValue = false;
sSave = id.innerText;
id.innerText = "";
}

function fnBeforePaste() {
event.returnValue = false;
}

function fnPaste(id) {
event.returnValue = false;
id.innerText = sSave;
}

</script>
use this script in html textbox

when asp:textbox
txtcpassword.Attributes.Add("onSelectStart", "return false;")
txtcpassword.Attributes.Add("onPaste", "return false;")use this code
it working fine in intenetexplorer(microsoft)
but not work in firefox
please give me a solution it's urgent