I found the menu bar will overwrite some content of first line. When I click the dropdown 'first', it will locate to the first list item, but it was overwritten by menu bar. I've try apply one solution Posted in jsbin, but failed.
original html is here.
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="utf-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<meta name="viewport" content="width=device-width, initial-scale=1">
<link rel="stylesheet" href="//maxcdn.bootstrapcdn.com/bootstrap/3.2.0/css/bootstrap.min.css">
<link rel="stylesheet" href="//maxcdn.bootstrapcdn.com/bootstrap/3.2.0/css/bootstrap-theme.min.css">
</head>
<body>
<div class="navbar navbar-default navbar-fixed-top" role="navigation">
<div class="container">
<div class="navbar-header">
<button type="button" class="navbar-toggle collapsed" data-toggle="collapse" data-target=".navbar-collapse">
<span class="sr-only">Toggle navigation</span>
<span class="icon-bar"></span>
<span class="icon-bar"></span>
<span class="icon-bar"></span>
</button>
<a class="navbar-brand" href="#">Bootstrap theme</a>
</div>
<div class="navbar-collapse collapse">
<ul class="nav navbar-nav">
<li class="dropdown">
<a href="#" class="dropdown-toggle" data-toggle="dropdown">Dropdown <span class="caret"></span></a>
<ul class="dropdown-menu" role="menu">
<li><a href="#first">first</a></li>
<li><a href="#end">end</a></li>
</ul>
</li>
</ul>
</div>
</div>
</div>
<ul>
<li id="first">first</li>
<li>a2</li><li>a3</li><li>a4</li><li>a5</li><li>a</li><li>a</li><li>a</li><li>a</li><li>a</li><li>a</li><li>a</li><li>a</li><li>a</li><li>a</li><li>a</li>
<li>a</li><li>a</li><li>a</li><li>a</li><li>a</li><li>a</li><li>a</li><li>a</li><li>a</li><li>a</li><li>a</li><li>a</li><li>a</li><li>a</li><li>a</li>
<li id="end">end</li>
</ul>
<script src="http://ajax.googleapis.com/ajax/libs/jquery/1.11.1/jquery.min.js"></script>
<script src="//maxcdn.bootstrapcdn.com/bootstrap/3.2.0/js/bootstrap.min.js"></script>
</body>
</html>
SOLUTION demo (as answer)