Solved: Vertical gap between two floated elements

I have two elements, one a title bar, and one a graphic. The title bar contains a floated element (h1), and the graphic itself is floated left. However between the two is a mystery gap. The gap has something to do with the floats because if they are removed, the gap disappears, however I do need the floats. I've tried various clearing methods after the titlebar div, and setting the font to 0, and the various margins to 0, but the gap remains.

The code passes w3c html and css validation checks. It displays *correctly* in IE6, but *not* in FF3.0.

I'd appreciate if you could show how to get the two elements to be adjacent and without the gap.

This has been stumping me and have researched this and still can't find what's happening.

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" 
 
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en">
<head>
<meta http-equiv="content-type" content="text/html; charset=utf-8" />
<title>SiteTitle</title>
<style type="text/css">
 
p, h1, h2 {margin-top: 0; padding: 0;}
 
html, body {margin:0; padding:0; left:0; margin-top:0;padding-top:0; font-size: 0;}
 
body {
  font: 100% Arial, Helvetica, sans-serif;
  font-size: small;
  margin: 0; 
  padding: 0;
  text-align: center; 
}
 
/* ===================Right Header Container=========================  */
 
 
#header_righttopbar {
  background-color: #000;
  height: 30px;
}
 
.header_title {
  float: left;   /* this must be floated */
  margin-top: 0px;
  padding-top: 0px;
  width: 55%;
}
 
#header_righttopbar h1 {
  text-align: left;
  color: #0f0;
}
 
#contentcolumn{   
  float: left;      
  color: #000;
  border-top: 0px;
  font-size: small;
}
 
#rightcolumn{         
  font-size: 0px;
  border-top: 0px;
  padding-top: 0px;
  margin-top: 0px;
  float: left;         /* if this is removed, gap will disappear - this must be 
 
floated  */ 
  width: 510px; 
  height: 339px;
  background-image: url("headerpic.jpg");
  background-repeat: no-repeat;
}
 
/* I've tried scattering this around, doesn't help */
.clearfloat { /* this class should be placed on a div or break element and should 
 
be the final element before the close of a container that should fully contain a 
 
float */
  clear:both;
  height:0;
  font-size: 1px;
  line-height: 0px;
}
 
</style>
 
</head>
 
<body>
  <div id="header_righttopbar">
    <h1 class="header_title">Title</h1>
  </div>
 
  <div id="rightcolumn">
    <p>testing 1 2 3</p>
  </div>
 
</body>
</html>

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headerpic.jpg