Some will say that cookies, at least most traditional cookies, are bad for your health and Web cookies have grown to become the same for your digital health. Created primarily to make it more convenient for users to revisit sites, again and again, the rather crude technology has been abused time and again to track users across the sites they visit. Browser makers are stepping up to fight such privacy invasions and the latest release of Firefox is designed to block another kind of cookie.
Recent updates to web browsers have focused on cross-site tracking cookies, those that follow you around even after you leave the original web page that generated it. Mozilla, however, names yet another kind of cross-site tracking it calls “Supercookie”, though it might as well be called “Zombie cookie”, too. In addition to following users around and fingerprinting them, these cookies are notorious for hiding in other parts of the browser and don’t get cleared along with other normal cookies.
Supercookies also take advantage of Firefox’s caching mechanism that tries to reduce the data bandwidth and time by reusing images or other resources that are shared or embedded across different sites. Unfortunately, this is also exactly how these Supercookies are able to fingerprint users by creating a unique identifier on one site that can then be checked again on another site when the same cached image is used.
Mozilla’s solution is to partition Firefox’s network state and local cache per site starting with version 85. This means that each site will now have its own image cache, for example, that only gets reused when visiting the same site but not when moving on to another site that uses the same image. This has the effect of pretty much isolating Supercookies but Mozilla does admit there is a very modest impact on page load times because of it.
Firefox 85 also spells the end for Adobe Flash, something that has been in the process for years already. It will no longer play Flash content and will offer no option to re-enable it. And you can forget about downgrading to an older version of Firefox to get around that as the Flash plugin itself has already stopped working at this point.