Mozilla has released Firefox 151, introducing new privacy-focused protections for Private Browsing Mode and stronger anti-fingerprinting defenses.
A new “End Private Session” feature for Firefox’s Private Browsing Mode, accessible through a fire-shaped icon next to the address bar, allows users to instantly wipe all data associated with the current private session without having to close the entire browser window.
Once activated and confirmed, Firefox clears browsing history, cookies, cached files, and other session data, then automatically launches a fresh private session. The capability addresses a long-standing usability issue with private browsing sessions, particularly for users who frequently switch between accounts or want to quickly erase session traces without interrupting active tabs or workflows.
Mozilla also expanded Firefox’s anti-fingerprinting protections under Standard Enhanced Tracking Protection, making it harder for websites and advertisers to identify users based on browser and device characteristics.
Browser fingerprinting is a tracking technique that relies on collecting subtle details such as screen resolution, installed fonts, hardware configuration, rendering behavior, and system settings to create a unique identifier for users even when cookies are blocked.
According to Mozilla, Firefox 151 reduces the number of users uniquely identifiable through common fingerprinting methods by approximately 14%, with macOS users seeing reductions of around 49%. The company did not provide technical implementation specifics.
Alongside the privacy enhancements, Firefox 151 also fixes multiple security vulnerabilities.
Among the most serious flaws patched are CVE-2026-8945, a high-severity sandbox escape vulnerability affecting Firefox and Firefox Focus for Android, and CVE-2026-8948, a same-origin policy bypass issue in the browser’s networking components. Mozilla also fixed CVE-2026-8947, a use-after-free flaw in WebIDL bindings that could potentially lead to memory corruption.
The release additionally addresses multiple memory safety vulnerabilities tracked as CVE-2026-8973 and CVE-2026-8975. Mozilla warned that some of these bugs showed evidence of memory corruption and could be exploited to execute arbitrary code.
Firefox 151 also introduces several secondary features, including the ability to merge PDFs directly inside Firefox’s built-in PDF viewer, cross-platform local profile backups on Linux, native macOS-style dropdown menus, and easier access to Firefox’s built-in translation tools.
Separately, Mozilla announced that its AI-powered “Shake to Summarize” feature is now rolling out to Android users in English after initially launching on iOS last year.
The feature allows users to shake their phones while viewing a webpage to generate a concise AI summary of articles under 5,000 words. Mozilla says the system uses on-device Apple Intelligence on supported iPhones, while other devices rely on Mozilla-hosted cloud infrastructure powered by the Mistral-Small language model.
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