Every time we delete the cookies and the cache on firefox, all the places where a super cookie could hide should be cleared as well: the HTTP cache, the image cache, the favicon cache, the HSTS cache, the OCSP cache, the style sheet cache, the font cache, the DNS cache, the HTTP Authentication cache, the Alt-Svc cache, and the TLS certificate cache.
And in case the folowing resources cache data, that caches should be cleared as well: pooled connections, prefetch connections, preconnect connections, speculative connections, and TLS session identifiers.
This will prevent super cookies from being recreated on the usual cookies location.