Mozilla/5.0 (Macintosh; Intel Mac OS X 10.6; rv:2.0b9pre) Gecko/20110109 Firefox/4.0b9pre ID:20110109030350 When I close a tab and try to undo it, the tab gets re-opened but placed into another tab group. That removes all other tabs, which will shock the user at the first time because he doesn't know where all the other tabs went to. Closing the tab switches back to the formerly tab group and all tabs are shown again. See the screencast: http://screencast.com/t/EFQdijLNxRoc A tab should be restored in the group it originally was located in.