* Ensure tabstrip widgets are temporarily removeable at browser init so the CUI placements are correctly applied * Shuffle placements during initialization to build the correct toolbars for the verticalTabs pref value * Notify on the 'tabstrip-orientation-change' topic when the verticalTabs pref changes and CUI placements have been updated * Add tests for switching tabstrip orientation, and for initializing in verticalTabs mode Differential Revision: https://phabricator.services.mozilla.com/D217161