We have
116 i.e. ASCII key code of
Keyboard F5 function key then stop its propagation by returning false inside the event handler.
We need to define the
onkeydown event handler within the body tag and simply
return false if the pressed key is F5 function key i.e. ASCII key code 116. <body onkeydown = "return(event.keyCode != 116);">
</body>