Here's the solution. You have to do it in Javascript. Ensure jQuery is loaded in your web pages (even the IFRAME/FRAME ones) and then apply this code:
<script type="text/javascript">
$(document).ready(function(){
// Disable backspace key except in fields.
$(document).keydown(function(e) {
var elid = $(document.activeElement).is('INPUT, TEXTAREA') ;
if (e.keyCode === 8 && !elid) {
if(e.ctrlKey) {
window.history.back();
} else { // disable backspace
e.preventDefault();
return false;
}
}
});
});
</script>
SOURCE: http://stackoverflow.com/a/17278620/105539
