Web Forms :: Enter Key Button Press Not Working In FireFox?

I have to set enter key event to text box, it work fine in IE, but not in firefox.

Here my code:

function DoClickToButton() {
var keycode = (event.keyCode ? event.keyCode : (event.which ? event.which : event.charCode));
alert(keycode);
if (keycode == 13) {
document.getElementById('<%=Button1.ClientID %>').click(); return false;
}
else {
return true
};
}