Firefox 90 SmartBlock 2.0 lets you log in with Facebook in Incognito mode

The most basic kind of protection against tracking that web browsers offer is Private Browsing mode, a.k.a. Incognito Mode that often blocks third parties and even the browser itself from tracking your movement through the Internet. This basic privacy measure isn't perfect, and it also causes some functionality to break. Unfortunately, one of those is being able to sign in to sites and services using a Facebook account, a problem that Firefox 90's new SmartBlock 2.0 is finally fixing.

Just like Google, Facebook offers a single sign-on or SSO functionality that removes the need to create and manage new accounts in every website or service. This functionality often uses scripts and cookies, the very things that Firefox's Private Browsing mode blocks. Complicating matters further is the fact that Facebook is included in Disconnect's list of known trackers that Firefox uses to determine which sites' scripts it should block.

Unfortunately, that leads to a broken experience for some sites that legitimately use Facebook to sign in to their service. These include the likes of Etsy, Pinterest, and more, making it inconvenient or even impossible for users to use these sites while browsing safely. In other words, Firefox users had to choose between protecting their privacy or using those sites, a decision they shouldn't have to make.

SmartBlock 2.0 now removes that limitation without sacrificing their privacy. Private Browsing mode still blocks all Facebook scripts, but when Firefox detects a Facebook sign-in, it unblocks only Facebook's login script so that you can proceed as normal.

This exception works only for third-party Facebook logins when browsing those sites in Private Browsing and Strict Mode. Sites that don't offer such a login but uses Facebook tracking will still have offending scripts blocked. It remains to be seen if Facebook will have any opposition to this method or if it will adjust its login mechanism to take advantage of the door that Firefox just opened for it.