The width of FileUpload control can't display correctly in FireFox?

The width of FileUpload control can't display correctly in FireFox?

I set the width of FileUpload1 control as 500px, it's OK in IE, but it can't display correctly in FireFox, it become short in FireFox, I hope it's Ok in two browsers, could you tell me how can do? thanks!

<%@ Page Language="C#" AutoEventWireup="true"  CodeFile="Default.aspx.cs" Inherits="_Default" %>

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

<html xmlns="http://www.w3.org/1999/xhtml" >
<head runat="server">
    <title>Untitled Page</title>
</head>
<body>
    <form id="form1" runat=& ...