A long time ago Firefox had a feature where clicking on the current tab switched focus to the last selected tab. Since the feature was removed, several add-ons have allowed you to restore this behavior, including:
Tab Mix Plus (https://addons.mozilla.org/hu/firefox/addon/tab-mix-plus/) with the option 'Switch to last selected tab when clicking current one'
But both extensions do not work with the new Firefox Quantum. Is there any way to restore this functionality?