* Fixup tree correctly after multiselected tabs are moved together by drag and drop on the horizontal tab bar or the [Move Tab Hotkeys](https://addons.mozilla.org/firefox/addon/move-tab-hotkeys/).
* Synchronize throbber animations after the sidebar is reopened.
* Keep highlighted appearance of multiselected tabs after the sidebar is reopened.
* Track and update overflow/underflow state correctly even if legacy overflow/underflow events are disabled completely.
* Restore "sticky" state of tabs correctly after tree restoration without cache.