I should be able to do anything in the listview for the advanced Message Search window that I can do in the threadpane for the main mailnews window. That means things like move, copy, tag, and mark (or at the very least, the things that cannot be accomplished via the buttons. Additionally, the menubar on Mac, which is enabled for this window, should be fully functional for all menus and menu item actions one might take while using the Message Search window. For Windows and Linux which do not have the permanent menubar, at least the "Message" context menu (and submenus) should be available.