Mozilla is rolling out a major update for Firefox 145 that introduces significant new anti-fingerprinting protections designed to make users harder to track across the web. The new “Phase 2” protections, which are being released tomorrow, will initially be available in Private Browsing Mode and when the Enhanced Tracking Protection (ETP) is set to “Strict.”
Fingerprinting is an invasive tracking technique used to identify users by collecting a wide range of subtle data points about their device. This can include operating system, installed fonts, screen resolution, CPU cores, and even how the graphics card renders images. Combined, these details create a unique “digital signature” that can be used to track a user’s activity across different websites, even when they block cookies or use a private browser.
Firefox has been working to combat this with its “Phase 1” protections, which already block many known fingerprinting scripts and reduce a user’s trackability. According to Mozilla, these existing measures reduced the percentage of users who could be uniquely fingerprinted from a baseline of 65% down to 35%.
The new “Phase 2” protections in Firefox 145 go a step further by actively spoofing or limiting the data that websites can request. The new measures include:
- The browser will now always report that the device has two processor cores.
- Access to local fonts is blocked. The browser will only use standard OS fonts, with exceptions for key language fonts (like Japanese, Korean, and Arabic) to ensure websites render correctly.
- The browser will report generic information for multi-touch support (0, 1, or 5) and will report the screen resolution as the screen height minus 48 pixels, obscuring the true dimensions of the dock or taskbar.
- The browser adds random “noise” to background images, but only when a site attempts to read the image data back, a common fingerprinting technique.
Mozilla says that with these additional “Phase 2” protections enabled, only 20% of users can still be uniquely fingerprinted and tracked. The company explained that it cannot block everything, as doing so would break legitimate website features, such as productivity tools that rely on real-time data. Users who experience usability problems can disable the new protections on a site-by-site basis.
Firefox 145 will be officially released on November 11, 2025. This release will also be the first to no longer offer a 32-bit version for Linux, as Mozilla is deprecating it due to low user demand.
