How do these add-ons work? For sites with an x-number of free articles a month I have come across an add-on that would clear all local storage for a particular

How do these add-ons work? For sites with an x-number of free articles a month I have come across an add-on that would clear all local storage for a particular paywalled site. Using a private browsing window would also allow me to view the site paywall-less in those cases, so I didn't need the add-on in those cases.