Single window with no chats opened
When Gajim is set to use single window for everything, the main window behaves wierdly when application is started and then first chat is opened. The tabs widget should not be hidden when there are no tabs, so it could act as a placeholder and preserve correct both window and roster size.
When first chat is opened, window changes its size to fit both roster and chat. But this is not very nice behavior. If tabs widget is not hidden there would be no need to change window size. The main window could be always maximized.