Ensure that popup window is configured to open in new window.
To get Microsoft CRM windows to launch in tabs, you'll need to configure the Internet Explorer Tabbed Browsing Settings so that pop-ups always open up in a new tab (located under Tools - Internet Options). With this setting checked, double-clicking a Microsoft
CRM record will launch it in a tab.
refer http://blog.sonomapartners.com/2006/05/post.html