网页在firefox下出现的问题


<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>登陆页面</title>
<style type="text/css">
<!--
.style1 {
color: #98B6FF;
font-weight: bold;
}
.style2 {
color: #828282;
font-weight: bold;
font-size: large;
}z
.style3{
   position:absolute;
   left: 1045px; 
   top: 620px ;
   width:152px;
   height:81px;
}
body {
background-image: url();
background-repeat: no-repeat;
background-color: #2DABFF;
}
.STYLE3 {font-size: 36}-->
</style>
</head><body>
<form name="loginForm" method="post" action="/login.do"><div><input type="hidden" name="org.apache.struts.taglib.html.TOKEN" value="3967f90f26471b01e0fbb75a01815e4a"></div>
  <table width="1100" height="677" border="0" align="center" background="../images/315.jpg" >    <tr valign="top" height="560" width="1100">
      <td width="517" height="580">&nbsp;</td>
      <td width="89"></td>
      <td width="346"></td>
      <td width="90"></td>
      <td width="36"></td>
    </tr>
    <tr height="39">
      <td height="21">&nbsp;</td>      <td><div align="left"><input type="text" name="username" size="8" value=""></div></td>
      <td>&nbsp;</td>
      <td rowspan="3"><label>
      <input name="imgfile" id="imgfile" type="image" src="../images/queding.jpg" >
      </label></td>
      <td>&nbsp;</td>
    </tr>
    <tr>
      <td height="7"></td>      <td></td>
      <td></td>
      <td></td>
    </tr>
    <tr height="39">
      <td height="28"><span class="STYLE3"></span></td>
      <td><div align="left" class="STYLE3"><input type="password" name="password" size="8" value=""></div>        </td>
      <td><span class="STYLE3"></span></td>      <td rowspan="2"><span class="STYLE3"></span></td>
    </tr>
    <tr height="39">
      <td height="28">&nbsp;</td>
      <td>&nbsp;</td>
      <td>&nbsp;</td>
      <td>&nbsp;</td>
    </tr>
  </table> 
</form>
</body>
</html>
代码如上，在username输入框那里输入字符一个字符占了二个字符的宽度，请问是怎么回事？