event 未在Firefox中定义，它破坏了您的代码。在测试 evt 之后放置它：

event is not defined in Firefox, it's breaking your code. Put it after testing for evt:

function isNumberKey(evt)
  {
    var e = evt || window.event; //window.event is safer, thanks @ThiefMaster
    var charCode = e.which || e.keyCode;                        
    if (charCode > 31 && (charCode < 47 || charCode > 57))
    return false;
    if (e.shiftKey) return false;
    return true;
 }

小提琴

下次检查错误控制台。 ：）

Check your error console next time. :)