Should you update to Firefox 158?
No: install Firefox 159.0.1 instead. Firefox 158 is a security update Mozilla released on 13 Oct 2026 for Mac, Windows and Linux. It fixes 77 security flaws, 0 rated critical and 30 high by Mozilla.[1] None of them is known to be used in attacks.
It has since been replaced by Firefox 158.0.1, released 20 Oct 2026, which includes all of its fixes.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 158, so there’s no reason to stop at this one. Software Update offers the newest version your device can run.
Is Firefox 158 still safe?
Not any more. The 3 updates since, up to Firefox 159.0.1, fix 172 security flaws that Firefox 158 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 77 security flaws, 0 rated critical and 30 high by Mozilla.[1] The 30 critical and high ones are:
| Flaw | Severity | What Mozilla calls it |
|---|---|---|
CVE-2026-109704 | High | Privilege escalation in the Application Update component |
CVE-2026-109705 | High | Sandbox escape, site isolation issue due to incorrect boundary conditions, use-after-free in the Networking component |
CVE-2026-109706 | High | Use-after-free in the Storage: IndexedDB component |
CVE-2026-109707 | High | Sandbox escape due to use-after-free in the Networking component |
CVE-2026-109708 | High | Sandbox escape due to incorrect boundary conditions in the Networking component |
CVE-2026-109709 | High | Information disclosure, privilege escalation in the Security: Process Sandboxing component |
CVE-2026-109710 | High | Use-after-free in the Graphics: Text component |
CVE-2026-109711 | High | Use-after-free in the Graphics: Canvas2D component |
CVE-2026-109712 | High | Sandbox escape due to uninitialized memory in the Graphics component |
CVE-2026-109713 | High | Use-after-free in the Crash Reporting component |
CVE-2026-109714 | High | Incorrect boundary conditions in the Layout component |
CVE-2026-109715 | High | Incorrect boundary conditions in the JavaScript Engine component |
CVE-2026-109716 | High | Incorrect boundary conditions in the JavaScript Engine component |
CVE-2026-109717 | High | Use-after-free in the DOM: Bindings (WebIDL) component |
CVE-2026-109718 | High | Use-after-free in the XML component |
CVE-2026-109719 | High | Race condition, use-after-free in the Graphics: CanvasWebGL component |
CVE-2026-109720 | High | JIT miscompilation in the JavaScript: WebAssembly component |
CVE-2026-109721 | High | Incorrect boundary conditions in the JavaScript Engine: JIT component |
CVE-2026-109722 | High | JIT miscompilation in the JavaScript Engine: JIT component |
CVE-2026-109723 | High | Integer overflow in the Layout: Text and Fonts component |
CVE-2026-109724 | High | Use-after-free in the DOM: Core & HTML component |
CVE-2026-109725 | High | Use-after-free in the DOM: Core & HTML component |
CVE-2026-109726 | High | Use-after-free in the SVG component |
CVE-2026-109727 | High | Use-after-free in the Audio/Video component |
CVE-2026-109728 | High | Use-after-free in the DOM: Animation component |
CVE-2026-109729 | High | Use-after-free in the JavaScript Engine: JIT component |
CVE-2026-109730 | High | Integer overflow in the Graphics component |
CVE-2026-109731 | High | Incorrect boundary conditions in the Graphics: Canvas2D component |
CVE-2026-109732 | High | Use-after-free in the DOM: Streams component |
CVE-2026-109733 | High | JIT miscompilation in the JavaScript Engine: JIT component |
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 158.0.1 or later.
157.0.1 vs 158
Firefox 157.0.1, released 6 Oct 2026, fixed 1 security flaw. Firefox 158 fixes 77 security flaws and includes the fixes before it, so going straight to 158 gets you both.
- Before: Firefox 157.0.1, 6 Oct 2026, 1 security flaw
- After: Firefox 158.0.1, 20 Oct 2026, 4 security flaws
- Firefox updates, every release and the latest version
- Updates, the latest version of everything HARD tracks
References
- ^ Mozilla. “Security Vulnerabilities fixed in Firefox 158”, 13 Oct 2026.