Firefox 159.0.1: install today's security point release

If Firefox is the browser you actually use at home, check the version again. On November 3, 2026, Mozilla shipped Firefox 159.0.1 to everyday Release users with a new security advisory.

This is a point release on the 159 line, not another jump from 158. Our Firefox 159.0 note covered the October 27 launch. 159.0 is no longer the finish line.

What Mozilla shipped

Mozilla’s Firefox 159.0.1 release notes say version 159.0.1 was first offered to Release channel users on November 3, 2026. The notes list everyday bug fixes (a hard-to-see tab attention dot, a command prompt window flashing on Windows when Firefox restarts to update, passkey sign-in on sites that share passkeys such as Facebook and Instagram, Windows crashes with some antivirus software, swapped WebGL colors on Linux, Cuba time zone data, and Settings text breaking mid-word) plus a security fix.

The security details are in MFSA 2026-123 (announced November 3, 2026, impact high), fixed in Firefox 159.0.1.

That advisory lists one named issue:

• CVE-2026-120572: Incorrect boundary conditions in the Layout: Block and Inline component. Mozilla reported it. Impact is high.

You do not need a memory-safety lecture. A high-impact advisory on a new Firefox build is enough reason to install.

If about:support still shows 159.0 or anything older, move to 159.0.1.

Why 159.0 is not enough anymore

Firefox 159.0, released October 27, fixed the large set in MFSA 2026-118. That install still mattered. It does not include the November 3 security fix in MFSA 2026-123.

Same habit every time:

1. Update
2. Fully quit and relaunch
3. Prove it with about:support

Downloaded is not running. The version line is the receipt.

How to update and verify on your computer

1. Open Firefox on the computer you actually browse with.
2. Check for updates.
   • Windows / Linux: Menu (three lines) > Help > About Firefox.
   • macOS: Firefox menu > About Firefox.
3. Stay on the About window until the download finishes. Firefox usually says it is downloading or ready to restart.
4. Restart to update when prompted. Do not click Later and keep working in old windows.
5. Fully quit if the version still looks old. Close every Firefox window. On Windows, confirm in Task Manager that no firefox.exe processes are left. On Mac, use Firefox > Quit Firefox. Then open Firefox again.
6. Verify with about:support. Type that into the address bar. In the Application Basics section, read Version. You want 159.0.1 (or a newer 159.0.x if Mozilla ships another point release after this article).
7. Repeat on other home computers that still run Firefox, including a laptop that stays open for days and any shared family computer.

If About Firefox does not offer 159.0.1 yet, wait a day for the rollout to reach you, then check again. If the updater seems stuck, download Firefox from Mozilla’s own site instead of a third-party download page.

Linux users who installed Firefox from their distribution’s packages should update through that package manager. Flatpak or Snap installs update through those tools. The goal is still 159.0.1.

Phone browsers are separate

Desktop Firefox updates do not patch Firefox on iPhone or Android. Those apps update through the App Store or Google Play on their own schedules. If you browse in Firefox on a phone, check the store listing and open the app once after it updates so the new build actually launches.

Do this / don’t do that

Do

• Open About Firefox, relaunch, and confirm about:support shows 159.0.1.
• Treat a high-impact security advisory as “install today,” not “install when I remember on Sunday.”
• Update Chrome, Edge, Brave, and Safari on their own if you use them. Updating Firefox does not update them.

Don’t

• Do not stop at 159.0 because you already “did the Firefox 159 update” last week.
• Do not assume a Windows restart alone applied 159.0.1 if about:support still shows 159.0.
• Do not download “Firefox offline installer” packs from third-party sites. Use Firefox’s own About window or Mozilla’s download page.

Bottom line

On November 3, 2026, Mozilla shipped Firefox 159.0.1 with MFSA 2026-123, a high-impact advisory for CVE-2026-120572 (release notes). On your own computer: install, relaunch, and verify about:support. Last week’s 159.0 update was worth doing. 159.0.1 is the new finish line.

Image: Official Firefox social image from firefox.com.