Notice while on Google\'s homepage, with no focus on any element, pressing BACKSPACE will put the focus into the search toolbar instead of navigating back.
I would bind an event handler to keydown and prevent the default action of that event if we're dealing with the backspace key outside of a textarea or input:
$(document).on("keydown", function (e) {
if (e.which === 8 && !$(e.target).is("input, textarea")) {
e.preventDefault();
}
});