Как это?
<html>
<head>
<meta charset="utf-8"/>
<title>Test</title>
<style type="text/css">
html, body, h1 {
margin:0px;
padding:0px;
}
header, nav, article, section, footer, address {
display: block;
}
header {
position:relative;
height: 50px;
width: 100%;
background-color:#2b2b2b;
}
footer{
height: 50px;
width:100%;
bottom: 0px;
position: fixed;
background: red;
border-top: 5px solid yellow;
}
#explorer{
position:relative; bottom:55px;
}
#sections{
width: 100%;
height: 100%;
bottom: 55px;
position:fixed;
top: 50px;
background: rgba(0,0,256,.5);
}
</style>
</head>
<body>
<header >
<h1>Test</h1>
</header>
<div id="explorer" >
<div id="sections" >
</div>
</div>
<footer>
/* Footer Content */
</footer>
</body>