Mozilla has been experimenting with new features in pre-beta versions of Firefox (Firefox Developer Edition on Windows, Mac and Linux and Firefox Aurora on Android) to offer more control over users' privacy, including updated Private Browsing ready for pre-beta testing. All major browsers offer some form of experience that is labeled 'private' but this is typically intended to solve the "local" privacy case, namely preventing others on a shared computer from seeing traces of users' online activity. But Mozilla is experimenting with ways to offer users even more control when they open Private windows.

The experimental Private Browsing enhancements ready for testing today actively block website elements that could be used to record user behavior across sites. This includes elements like content, analytics, social and other services that might be collecting data without a user's knowledge. In some cases, websites might appear broken when elements that track behavior are blocked, but users can always unblock these if they want to view the website normally. Private Browsing in pre-beta Firefox also has a Control Center that contains important site security and privacy controls in a single place.

Add-ons provide virtually limitless possibilities for how users can customize the look and functionality of Firefox. However, add-ons also have access to information Firefox manages and Mozilla's engineers are working to help make third-party add-ons a safer experience. Add-ons may have the ability to create unwanted toolbars or buttons, collect information, change users' search settings or inject ads or malware into their devices. Mozilla has worked with developers and created a process that attempts to verify that add-ons installed in Firefox meet the guidelines and criteria they have developed to ensure they’re safer. Starting with this release, add-on verification is enforced by default in pre-beta Firefox.

Electrolysis runs Web content in a separate process from the main browser and is enabled by default for most pre-Beta users. Performance improves with Electrolysis because the main browser process remains responsive to a user's input even when the content process is doing work. Some Firefox add-ons may not currently be compatible with Electrolysis and might not work as expected or at all.