On fr.wikipedia.org, when in the abusefilter log ( https://fr.wikipedia.org/wiki/Sp%C3%A9cial:Journal_du_filtre_antiabus ), when clicking on the drop-down settings menu, named (in French) "Rechercher dans le journal des filtrages", this drop-down menu doesn't open on the first try. When the bugs occurs, a reload/F5 often (but not always) solve the problem.
Bug encountered several times, on Firefox 86.0.1. No ad blocker enabled.