We can disable F5 Keyword using Javascript like this
<%@ Page Language="C#" AutoEventWireup="true" CodeFile="CloseBrowserTest.aspx.cs" Inherits="CloseBrowserTest" %>
<!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 id="Head1" runat="server">
<title>Untitled Page</title>
<script type="text/javascript">
document.attachEvent("onkeydown", my_onkeydown_handler)
function my_onkeydown_handler()
{
if(event.keyCode == 116)
{
event.keyCode = 0;
event.returnValue = false;
}
}
</script>
</head>
<body onload="return my_onkeydown_handler()">
<form id="form1" runat="server">
<div>
</div>
</form>
</body>
</html>
Chandradev's Blog 
nice code
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