I use a three-column design with fixed left and right column and variable middle column. When window is resized, the contents of the left column are shown on top of the middle column, the left column is empty. Solved by refresh. Problem does not occur in Firefox 4.01.

Code CSS:
@charset "iso-8859-1";
.clear
{
	clear: both;
	padding-bottom: 1px;
	margin-bottom: -1px;
}
.hide
{
	display: none !important;
}
.inside
{
	padding: 0 1em;
}
ul, ol, dl, p, h1, h2, h3, h4, h5, h6
{
	margin-top: 14px;
	margin-bottom: 14px;
	padding-top: 0;
	padding-bottom: 0;
}
h1
{
	font-size: 220%;
}
h2
{
	font-size: 190%;
}
h3
{ color: navy; font-size: 160%; }
h4
{ color: navy; font-size: 130%; }
h5
{ color: navy; font-size: 100%; }
h6
{
	font-size: 80%;
}
a, a:link, a:visited, a:active
{
	text-decoration: underline;
}
a:hover
{
	text-decoration: none;
}
code
{
	font-family: "Courier New", Courier, monospace;
}
label
{
	cursor: pointer;
}
td, th
{
	vertical-align: top;
}
table
{
	font-size: 100%;
}
body
{ margin: 0;	
	font-size: 100.1%; border-width: 0;	
}
#pageWrapper
{ min-width: 40em;	
	width: auto; border: solid 1px #fff; }
* html #pageWrapper
{
		word-wrap: break-word;
}
#masthead
{ border-width: 0 0; padding: 0; border-color: #fff; border-style: solid; }
#masthead h1
{
	padding: 0;
	margin: 0;
}
#outerColumnContainer
{
	border-left: 14em solid #fff;
	border-right: 14em solid #fff;
}
#innerColumnContainer
{ border-width: 0 1px; margin: 0 -1px;
	width: 100%; z-index: 1; border-color: #fff; border-style: solid; }
#leftColumn, #middleColumn, #rightColumn, * html #SOWrap
{
	overflow: visible;
	position: relative;
}
#SOWrap
{
	float: left;
	margin: 0 -1px 0 0;
	width: 100%;
	z-index: 3;
}
#middleColumn
{ float: right; margin: 0 0 0 -1px; width: 100%; z-index: 5; }
#leftColumn
{
	float: left;
	margin: 0 1px 0 -14em;
	width: 14em;
	z-index: 4;
}
#rightColumn
{
	float: right;
	width: 14em;
	margin: 0 -14em 0 1px;
	z-index: 2;
}
#footer
{ border-width: 1px 0 0; padding: 0.5em 0.5em 0 ; border-color: #fff; border-style: solid;0.5em 0;
}
 
p.fontsize-set
{ font-size-adjust: 80%; text-align: center; }
p.fontsize-set img
{
	border-width: 0;
}
#menuh
	{ font-family: arial, helvetica, sans-serif; width: auto; float: left; }
 
#menuh a
	{ text-align: center; width: auto; display:block; white-space:nowrap; margin:0; padding: 0.3em 0.3em 0.3em 0.1em; border-color: rgb(92,150,181); border-style: solid; border-width: 0 1px 0 0; }
 
#menuh a:link, #menuh a:visited, #menuh a:active	/* menu at rest */
	{ color: navy; background-color: aqua; text-decoration:none; width: auto; }
 
#menuh a:hover	/* menu at mouse-over  */
	{
	color: white;
	background-color: rgb(98,129,176);
	text-decoration:none;
	}	
 
#menuh a.top_parent, #menuh a.top_parent:hover  /* attaches down-arrow to all top-parents */
	{ background-image: url(../images/navdown_black.gif); background-position: right center; background-repeat: no-repeat; width: auto; }
 
#menuh a.parent, #menuh a.parent:hover 	/* attaches side-arrow to all parents */
	{ background-image: url(../images/nav_black.gif); background-position: right center; background-repeat: no-repeat; }
 
#menuh ul
	{ list-style:none; margin:0; padding:0; float:left; width:9em; border-right-width: 1px; border-left-width: 1px; outline-width: thin;	/* width of all menu boxes */
	}
 
#menuh li
	{ position:relative; min-height: 1px; vertical-align: bottom; }
 
#menuh ul ul
	{ position: absolute; z-index:500; top:auto; display:none; padding: 1em; margin:-1em 0 0 -1em; }
 
#menuh ul ul ul
	{ top:0; left: 100%; }
 
div#menuh li:hover
	{
	cursor:pointer;
	z-index:100;
	}
 
div#menuh li:hover ul ul,
div#menuh li li:hover ul ul,
div#menuh li li li:hover ul ul,
div#menuh li li li li:hover ul ul
{display:none;}
 
div#menuh li:hover ul,
div#menuh li li:hover ul,
div#menuh li li li:hover ul,
div#menuh li li li li:hover ul
{display:block;}
.s1 { float: left; margin-right: 12px; margin-bottom: 8px; margin-top: 8px; }
.s2 { }
.s3 { float: right; margin-left: 12px; margin-bottom: 8px; margin-top: 8px; }
.vnav
{ margin: 0; }
.vnav ul, .vnav ul li
{ background-color: aqua; margin: 0; padding: 0; list-style-type: none; display: block; }
.vnav ul
{ background-color: aqua; border: solid 0 #fff; }
.vnav ul li
{ background-color: aqua; border-bottom: 0 solid #fff; }
.vnav ul li, .vnav ul li a
{
	margin: 0;
	display: block;
	padding: 0;
	line-height: normal;
}
.vnav ul li a
{ background-color: aqua; display: block; padding: 2px 5px 3px; }
.vnav ul li a, .vnav ul li a:link, .vnav ul li a:visited, .vnav ul li a:active, .vnav ul li a:hover
{
	text-decoration: none;
	border: solid 1px white;
	cursor: pointer;
}
.vnav h3
{
	margin-bottom: 0;
	padding-bottom: 0;
	font-size: 126%;
}
* html .vnav ul li a
{ background-color: aqua; height: 0.01%; }
* html .vnav ul
{ background-color: aqua; position: relative;	/* IE needs this to fix a rendering problem */
}
#pageWrapper, #masthead, #innerColumnContainer, #footer, .vnav ul, .vnav ul li, .hnav, .hnav ul li a
{
	border-color: rgb(92,150,181);
}
html, body
{
	background-color: white;
	color: black;
	font-family: arial, helvetica, sans-serif;
}
#pageWrapper
{
	font-size: 80%;	
}
#masthead
{
	background-color: white;
	color: #fff;
}
#outerColumnContainer
{
	border-left-color: white;
	border-right-color: white;
	background-color: #fff;
}
.vnav ul li a:link, .vnav ul li a:visited, .vnav ul li a:active
{
	text-decoration: none;
	background-color: rgb(218,235,249);
	color: navy;
}
#rightColumn .vnav ul li a:link, #rightColumn .vnav ul li a:visited, #rightColumn .vnav ul li a:active
{ font-size: small; background-color: aqua; text-align: center; }
.vnav ul li a:hover, #rightColumn .vnav ul li a:hover
{
	text-decoration: none;
	background-color: rgb(98,129,176);
	color: #fff;
}
#rightColumn .inside
{
	font-size: 100%;
}
#rightColumn .inside .vnav
{
	font-size: 110%;
}
#footer
{
	background-color: white;
	color: rgb(92,150,181);
	text-align: center;
}

Have searched posts on this site to no avail. Anyone has a clue?