The 'Integer Only Validator' doesn't work in FireFox (tested on 184.108.40.206), it seems to work only in IE (tested on IE 6).
The problem is the way the keyboard event is treated. Attached is a fix to make it work in both Firefox and IE.
The only change when using it is to pass a new argument. Thus, to use it you should do it as 'keyPressNumber(false, event);'.