Today, with the launch of Firefox 90, we are excited to announce a new version of SmartBlock, our advanced tracker blocking mechanism built into Firefox Private Browsing and Strict Mode. SmartBlock 2.0 combines a great web browsing experience with robust privacy protection, by ensuring that you can still use third-party Facebook login buttons to sign in to websites, while providing strong defenses against cross-site tracking.

At Mozilla, we believe that privacy is a fundamental right. As part of the effort to provide a strong privacy option, Firefox includes the built-in Tracking Protection feature that operates in Private Browsing windows and Strict Mode to automatically block scripts, images, and other content from being loaded from known cross-site trackers. Unfortunately, blocking such cross-site tracking content can break website functionality.

Ensuring smooth logins with Facebook

Logging into websites is, of course, a critical piece of functionality. For example: many people value the convenience of being able to use Facebook to sign up for, and log into, a website. However, Firefox Private Browsing blocks Facebook scripts by default: that’s because our partner Disconnect includes Facebook domains on their list of known trackers. Historically, when Facebook scripts were blocked, those logins would no longer work.

For instance, if you visit etsy.com, the front page gives the following options to sign in, including a button to sign in using Facebook’s login service. If you click on the Enhanced Tracking Protection shield in the address bar, ()and click on Tracking Content, however, you will see that Firefox has automatically blocked third-party tracking content from Facebook to prevent any possible tracking of you by Facebook on that page:

Prior to Firefox 90, if you were using a Private Browsing window, when you clicked on the “Continue with Facebook” button to sign in, the “sign in” would fail to proceed because the third-party Facebook script required had been blocked by Firefox.

Now, SmartBlock 2.0 in Firefox 90 eliminates this login problem. Initially, Facebook scripts are all blocked, just as before, ensuring your privacy is preserved. But when you click on the “Continue with Facebook” button to sign in, SmartBlock reacts by quickly unblocking the Facebook login script just in time for the sign-in to proceed smoothly. When this script gets loaded, you can see that unblocking indicated in the list of blocked tracking content:

SmartBlock 2.0 provides this new capability on numerous websites. On all websites where you haven’t signed in, Firefox continues to block scripts from Facebook that would be able to track you. That’s right — you don’t have to choose between being protected from tracking or using Facebook to sign in. Thanks to Firefox SmartBlock, you can have your cake and eat it too!

And we’re baking more cakes! We are continuously working to expand SmartBlock’s capabilities in Firefox Private Browsing and Strict Mode to give you an even better experience on the web while continuing to provide strong protection against trackers.

Thank you

Our privacy protections are a labor of love. We want to acknowledge the work and support of many people at Mozilla that helped to make SmartBlock possible, including Paul Zühlcke, Johann Hofmann, Steven Englehardt, Tanvi Vyas, Wennie Leung, Mikal Lewis, Tim Huang, Dimi Lee, Ethan Tseng, Prangya Basu, and Selena Deckelmann.