The Tor Project has paused new feature development for Tor Browser 16 as developers work through more than 250 changes inherited from Firefox ESR 153 to ensure they do not weaken the browser's privacy and anonymity protections.
The announcement accompanied the release of Tor Browser 16.0a9, the latest alpha build intended for testing rather than everyday use.
The update explains that the project is prioritizing a large-scale audit of upstream Firefox changes before promoting Tor Browser 16 to its stable release. While Tor Browser 16.0a9 includes Firefox's latest security updates, the project stressed that the focus is on validating compatibility with Tor's stricter threat model rather than adding new functionality.
Tor Browser is a privacy-focused web browser developed by the Tor Project that routes internet traffic through the Tor network to help protect users' identities and resist tracking and surveillance. Because it is built on Firefox while maintaining hundreds of Tor-specific modifications, every major Firefox release requires extensive review to ensure upstream changes do not introduce privacy regressions.
According to the project, developers have already flagged more than 250 Firefox changes for review and resolved roughly half of them. These are not security vulnerabilities but rather code changes that must be examined to verify compliance with Tor's anonymity model. New feature development has been temporarily suspended to allow the team to complete the audit and stabilize the browser before Firefox ESR 140 reaches end-of-life status on October 13.
The effort follows Tor's transition to building alpha releases on Firefox beta versions, allowing developers to identify compatibility issues much earlier in the release cycle. The project said rebasing hundreds of Tor-specific patches is now shared across all eight members of the browser team instead of relying on only a few developers, reducing the risk of burnout and making it easier to address regressions incrementally.
Google will soon require updated applications to target a newer Android API level, creating a hard deadline for releasing Tor Browser 16. To remain within Google Play's 100 MB package-size limit, Tor developers modified Firefox's build process so the large omni.ja resource archive is compressed with XZ and decompressed at runtime, reducing the application size by approximately 3 MB. The project also said Tor Browser for Android now contains only one library classified as a tracker, Mozilla Telemetry, which remains disabled at runtime and may be removed in a future release.
The latest alpha includes updates to Firefox ESR 153, GeckoView 153, NoScript 13.6.30, and Go 1.26.5, as well as numerous Tor-specific fixes and interface changes.
Tor Browser 16.0a9 is available through the project's alpha release channel. The Tor Project reiterated that alpha builds are intended solely for testing and may contain bugs affecting usability, security, and privacy. The team is targeting a stable Tor Browser 16 release in September, approximately one month earlier than last year's schedule.
Leave a Reply