User Agent: Mozilla/5.0 (Windows NT 6.1; rv:5.0) Gecko/20100101 Firefox/5.0 Build ID: 20110615151330 Steps to reproduce: Install Firefox 5.0 . Open a new window. Enter any website address say mozilla.com . I wanted to close the tab and open a new tab. Actual results: When i wanted to close that tab and open a new one there was no close tab button available. There was no other option to close the tab in the File or Edit Menu options either. The Close Tab button appeared only after a second tab was opened. Expected results: There should have been a close tab button when only a single tab is open. And on pressing the close tab button it should either populate a new tab with about-blank or a homepage set by the user or show no tab at all.