Mozilla Firefox Nightly159.0a1

Browse websites, use online services, and access everyday internet content with Mozilla Firefox Nightly on a Mac. It brings upcoming Firefox features to users who want an early look at changes before they reach regular releases. As freeware in the Internet & Browsers category, it suits general users, home computing, and routine web access.

Nightly provides a pre-release browser for exploring future Firefox work across desktop, Android, and iOS development. It lets testers try about-to-be-released functionality in the most stable build among Firefox’s pre-release versions, while also providing a practical environment for checking performance and behavior. The browser is useful to enthusiasts, developers, and other testers who want to encounter new features early and report problems before wider release.

The macOS edition supports both Intel and Apple Silicon hardware, but Firefox Nightly no longer supports macOS 10.14 or earlier. The current version is 159.0a1,2026-10-02-21-18-53. It is an unstable testing and development platform, so behavior can change as new work enters the browser.

By default, Nightly sends data to Mozilla and sometimes its partners to help investigate issues and evaluate ideas. It updates approximately once or twice daily, keeping the testing build close to ongoing development. Users who find something malfunctioning can provide feedback to help refine performance and functionality for a later stable release.