Mozilla has released Firefox 155 and Thunderbird 155 as both projects switch to a fortnightly release schedule, meaning updates will now land roughly every two weeks rather than the previous slower cadence. Mozilla announced the accelerated pace for Firefox in July, with MZLA subsequently confirming Thunderbird would follow suit; users who dislike frequent updates are advised to move to the Extended Support Release (ESR) rather than disabling automatic updates altogether.

Firefox 155's headline changes are mostly AI-related, including a wider rollout of the "Smart Window" feature and improved LLM-assisted tab-group naming, alongside a new (though not yet widely available) tracker-blocking counter in the address bar, reorderable browser containers, faster page loading via Happy Eyeballs v3, better game-controller navigation, and larger PDF print scaling. An "AI kill switch" introduced in Firefox 148 remains available for those who want to disable such features, while this release adds local translation support for Marathi and Urdu. Thunderbird 155 focuses on more practical additions, including new policy controls for its QR code sync-export feature and experimental settings, a default address book option, improved S/MIME encrypted attachment handling, and various OAuth authentication enhancements.