Are security updates downloaded automatically

Yes. This v152.0.1 you're currently using went out Thursday, and was scheduled to update everyone withing a day or so. Most people were already running the latest version by Friday or Saturday. There might be a setting that won't apply the update for you immediately, only after restarting, but in that case you'll get notifications about any updates pending. It will be nonetheless downloaded in the background anyway, and just waiting for the next convenient restart — if you've configured so. There might be custom organization or enterprise settings only enforcing manual updates, but that's a specific situation that would be visibly noted in your "About Firefox" dialog if that's your case.