Firefox 75 will purge site data if associated with tracking cookies

[harlan4096]

Mozilla plans to integrate a change in Firefox 75 to improve the privacy of users of the web browser further. The organization plans to purge site data of sites associated with tracking cookies automatically in the browser.

Firefox ships with tracking protection enabled and while that is a good first line of defense against tracking on the Internet, it is based on a list of known tracking sites which means that it does not protect against all site-based tracking attempts.

Tracking sites not on the list are not blocked and may therefore set cookies and use other means of tracking users. A relatively new way of tracking users came to light recently; called first-party tracking, it is making use of CNAME redirects to bypass most built-in and extension-based blockers.

Basically, what happens is that a subdomain of the site is redirected but since this happens after the initial blocking, it is not prevented by most blocking tools. The popular uBlock Origin extension for Firefox handles these by performing look-ups of these redirects and blocking resources identified as trackers or ad-servers.

Mozilla plans to integrate functionality into Firefox to purge cookies and other site data of tracking domains automatically which addresses first-party tracking attempts. The bug 1599262 on the organization's bug tracking site Bugzilla provides information on the new protection:

Purge site data when site identified via old tracking cookies

Identify sites that set tracking cookies, remove those cookies (and other site data) if the site has not been interacted with in 30 days.

Firefox will check if sites that set tracking cookies are available; if they are and if the site has not been interacted with for 30 days, they are deleted.
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