Follow-up for the discussion start in Bug 729674. Currently Lightning adds the Calendar Tab and Task Tab to the new tab toolbar. Unfortunately the buttons cannot be removed. I'd ask to allow to move/customize them. For me the following would be useful: The mail toolbar and the tab toolbar share the same set of buttons. There is one set of Calendar/Task Tab buttons that can be customized. The user can display the button on the tab toolbar or the mail toolbar or hide the button. By default the buttons are shown on the tab toolbar. Each of the calendar toolbar and the task toolbar get its own Calendar/Task Tab buttons. By default the buttons are not shown. Reason: I want to customize Thunderbird to have the buttons in the same position on all toolbars for quick access.