It looks like finalize was meant to destroy the highlighter front **and** actor, but the actor wasn't destroyed. Also calling finalize or destroy didn't make much diffence on both sides. Stop using "finalize" manually from the frontend, instead rely on Front's destroy method to emit the oneway+release "finalize" request, which would destroy both front and actor. Differential Revision: https://phabricator.services.mozilla.com/D306796