Mozilla Firefox is a free, open-source browser that draws pages with its own Gecko engine rather than a Chromium base. This page covers version 159.0 for Windows, a 90.2 MB installer released on October 27, 2026. The file is fetched straight from Mozilla's server at download-installer.cdn.mozilla.net.
Gecko and an MPL-2.0 licence define Firefox
Firefox is developed by the Mozilla Foundation and its subsidiary, the Mozilla Corporation. It uses the Gecko layout engine, which implements current and anticipated web standards. The code is released under the MPL-2.0 licence, and Firefox is free.
In 2017 the project began folding in new technology under the code name Quantum. The stated aims were more parallelism and a more intuitive interface. Firefox also uses SpiderMonkey as its JavaScript engine.
A session in version 159.0
Day to day, Firefox works as a standard tabbed browser on Windows 7 or newer. Version 159.0 makes saved passwords available from the sidebar by default, so you no longer need to add the Passwords tool first.
The release also adds Smart Window watches, which can monitor a page for changes such as price drops or restocks. You type /watch in the chat, and Firefox sends a desktop notification on a match. Watches are managed from the Tasks button in the toolbar. This feature is part of a progressive roll out, so it may not appear for everyone yet.
The fixes cover file uploads and memory use. The upload dialog now opens in the folder last used for uploads rather than the last save location. Memory growth with sites like the Zoom web app left open in a minimized window was also fixed.
Firefox against Chrome, Edge, Brave, Opera and Tor
The alternatives are Google Chrome, Microsoft Edge, Brave, Opera GX Stable, Opera Stable and Tor Browser. This page does not rank them. What sets Firefox apart is its engine and licence: it runs on Gecko under MPL-2.0 and is built by a community of thousands.
Firefox sits in the lightweight browsers category. It is available officially for Windows, macOS and Linux, with unofficial ports for FreeBSD, OpenBSD, NetBSD, illumos and Solaris.
What's new in 159.0
Version 159.0 arrived on October 27, 2026. It adds passwords to the sidebar by default and Smart Window page watches in a progressive roll out. It also fixes bookmark import from signed-in Google Chrome profiles.
Mozilla Firefox (en-US) pros and cons
Pros
- Free and open source under the MPL-2.0 licence
- Uses the Gecko engine rather than a Chromium base
- Runs on Windows 7 or newer, plus macOS and Linux
- Installer is served from Mozilla's official host
- Version 159.0 puts saved passwords in the sidebar by default
Cons
- The 90.2 MB download is larger than a bare-bones installer
- Smart Window watches are in a progressive roll out and may not be available to every user
- Visual previews are not shown on this page
Is Mozilla Firefox (en-US) safe?
The Windows installer comes from Mozilla's own server, download-installer.cdn.mozilla.net, so the file never passes through us. Firefox is published by Mozilla under the MPL-2.0 open-source license, which means its code is open to public review. Before running the installer, confirm that the address it was fetched from matches that server.
How to install Mozilla Firefox (en-US)
- Press the download button to get the official file.
- Run the installer you saved and confirm the Windows security prompt if the publisher matches.
- Follow the setup steps, then start Mozilla Firefox (en-US) from the Start menu.
