* 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