Should you update to Firefox 158.0.1?
No: install Firefox 159.0.1 instead. Firefox 158.0.1 is a security update Mozilla released on 20 Oct 2026 for Mac, Windows and Linux. It fixes 4 security flaws, 0 rated critical and 2 high by Mozilla.[1] None of them is known to be used in attacks.
It has since been replaced by Firefox 159, released 27 Oct 2026, which includes all of its fixes.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 158.0.1, so there’s no reason to stop at this one. Software Update offers the newest version your device can run.
Is Firefox 158.0.1 still safe?
Not any more. The 2 updates since, up to Firefox 159.0.1, fix 168 security flaws that Firefox 158.0.1 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 4 security flaws, 0 rated critical and 2 high by Mozilla.[1] The 2 critical and high ones are:
| Flaw | Severity | What Mozilla calls it |
|---|---|---|
CVE-2026-113399 | High | Incorrect boundary conditions in the SVG component |
CVE-2026-113470 | High | Cryptographic issue in the Security Block-lists, Allow-lists, and other State 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 159 or later.
158 vs 158.0.1
Firefox 158, released 13 Oct 2026, fixed 77 security flaws. Firefox 158.0.1 fixes 4 security flaws and includes the fixes before it, so going straight to 158.0.1 gets you both.
- Before: Firefox 158, 13 Oct 2026, 77 security flaws
- After: Firefox 159, 27 Oct 2026, 167 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 158.0.1”, 20 Oct 2026.