Add the following javascript code in your aspx page.

Code:

<head id="Head1" runat="server">

<script type="text/javascript">

//disabling browser back button for mozila

function noBack(){window.history.forward()}

noBack();

window.onload=noBack;

window.onpageshow=function(evt){if(evt.persisted)noBack()}

window.onunload=function(){void(0)}

</script>

</head>