This involves changing moveToAnchor to be allowed while the popup is showing. This change allows the buttons within the tab to use the normal algorithm for determining the tooltip position. This also fixes bug 1695900 so that tooltips for items in bookmarks menus also appear offset as well. Only the main tab and bookmarks on the toolbar appear aligned with the button's bottom edge.
Differential Revision: https://phabricator.services.mozilla.com/D115558