You find such an option in the drop-down of the sidebar. See also https://support.mozilla.org/en-US/kb/use-firefox-sidebar-access-bookmarks-history-synced

I would prefer it if you don't use reviews for questions anymore as this isn't the right place for it. Either use GitHub issues for this or use these ways: https://github.com/Croydon/vertical-tabs-reloaded#contact