Should you update to Firefox 159?
No: install Firefox 159.0.1 instead. Firefox 159 is a security update Mozilla released on 27 Oct 2026 for Mac, Windows and Linux. It fixes 167 security flaws, 0 rated critical and 108 high by Mozilla.[1] None of them is known to be used in attacks.
It has since been replaced by Firefox 159.0.1, released 3 Nov 2026, which includes all of its fixes. If you’re on an older version, install that instead.
Should you update?
No: install Firefox 159.0.1 instead. Firefox 159.0.1 came out on 3 Nov 2026 and includes every fix in Firefox 159, so there’s no reason to stop at this one. Software Update offers the newest version your device can run.
Is Firefox 159 still safe?
Not any more. Firefox 159.0.1 fixes 1 security flaw that Firefox 159 doesn’t, and each became public the day its fix shipped. Installing it is safe: get it only from Firefox’s own About window (☰ menu → Help → About Firefox), never from a link in an email, text or pop-up.
What it fixes
Mozilla lists 167 security flaws, 0 rated critical and 108 high by Mozilla.[1] The 108 critical and high ones are:
| Flaw | Severity | What Mozilla calls it |
|---|---|---|
CVE-2026-117860 | High | Same-origin policy bypass in the DOM: Navigation component |
CVE-2026-117861 | High | Sandbox escape in the DOM: Navigation component |
CVE-2026-117862 | High | Privilege escalation due to incorrect boundary conditions in the Networking component |
CVE-2026-117863 | High | Information disclosure due to uninitialized memory in the Audio/Video component |
CVE-2026-117864 | High | Sandbox escape in the Form Manager component |
CVE-2026-117865 | High | Use-after-free in the JavaScript: GC component |
CVE-2026-117866 | High | Privilege escalation due to use-after-free in the Graphics: Canvas2D component |
CVE-2026-117867 | High | Use-after-free in the Layout component |
CVE-2026-117868 | High | Sandbox escape in the DOM: Networking component |
CVE-2026-117869 | High | Use-after-free in the DOM: Core & HTML component |
CVE-2026-117870 | High | Use-after-free in the JavaScript Engine component |
CVE-2026-117871 | High | Invalid pointer in the Graphics component |
CVE-2026-117872 | High | Use-after-free in the JavaScript: Standard Library component |
CVE-2026-117873 | High | Incorrect boundary conditions in the Audio/Video: Playback component |
CVE-2026-118005 | High | Use-after-free in the WebRTC: Signaling component |
CVE-2026-117874 | High | Use-after-free in the Internationalization component |
CVE-2026-117875 | High | Use-after-free in the Layout: Scrolling and Overflow component |
CVE-2026-117876 | High | Use-after-free in the Layout: Text and Fonts component |
CVE-2026-118006 | High | Privilege escalation due to use-after-free in the WebRTC: Signaling component |
CVE-2026-117877 | High | Use-after-free in the Layout: Text and Fonts component |
CVE-2026-118007 | High | Use-after-free in the JavaScript: GC component |
CVE-2026-117878 | High | Other issue, use-after-free in the Storage: IndexedDB component |
CVE-2026-117879 | High | Incorrect boundary conditions in the Layout: Tables component |
CVE-2026-118008 | High | Privilege escalation in the DOM: Navigation component |
CVE-2026-117880 | High | Use-after-free in the XML component |
CVE-2026-118009 | High | Integer overflow, use-after-free in the Graphics: Text component |
CVE-2026-117881 | High | Use-after-free in the DOM: Core & HTML component |
CVE-2026-117882 | High | Use-after-free in the Layout component |
CVE-2026-117883 | High | Use-after-free in the DOM: HTML Parser component |
CVE-2026-117884 | High | Use-after-free in the Networking component |
| and 78 more | ||
How to update, and how long it takes
A minute or two. Firefox restarts and reopens your tabs.
- Open Firefox’s About window.Open the ☰ menu → Help → About Firefox. Firefox checks for the update and downloads it.
- Click Restart to update Firefox.Firefox reopens your windows and tabs. Until it restarts, the old, unfixed version keeps running.
- Leave automatic updates on.In Settings → General → Firefox Updates, keep “Automatically install updates” selected.
To check it worked: The ☰ menu → Help → About Firefox shows the version. It should say 159.0.1 or later.
158.0.1 vs 159
Firefox 158.0.1, released 20 Oct 2026, fixed 4 security flaws. Firefox 159 fixes 167 security flaws and includes the fixes before it, so going straight to 159 gets you both.
- Before: Firefox 158.0.1, 20 Oct 2026, 4 security flaws
- After: Firefox 159.0.1, 3 Nov 2026, 1 security flaw
- Firefox updates, every release and the latest version
- Updates, the latest version of everything HARD tracks
References
- ^ Mozilla. “Security Vulnerabilities fixed in Firefox 159”, 27 Oct 2026.