Code:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html>
	<head>
		<title id="page-title">Test Page</title>
			
		<link rel="stylesheet" type="text/css" href="js/extjs/resources/css/ext.css" />
		
		<script type="text/javascript" src="js/extjs/ext-core-debug.js"></script> 
		<script type="text/javascript" src="js/extjs/ext-all-debug.js"></script> 

		<script type="text/javascript">
			Ext.onReady(function() {
				var panel = new Ext.tab.TabPanel({
					renderTo: Ext.getBody(),
					width: 600,
					height: 400,
					title: 'Test',
					items: [{
						title: 'Test 1',
						closable: true
					}, {
						title: 'Test 2',
						closable: false
					}]
				});
			});		
		</script>
	</head>
	<body>
	</body>
</html>
Neither tab is closable.