Should you update to Firefox 156?
No: install Firefox 159.0.1 instead. Firefox 156 is a security update Mozilla released on 15 Sep 2026 for Mac, Windows and Linux. It fixes 73 security flaws, 0 rated critical and 27 high by Mozilla.[1] None of them is known to be used in attacks.
It has since been replaced by Firefox 157, released 29 Sep 2026, which includes all of its fixes.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 156, so there’s no reason to stop at this one. Software Update offers the newest version your device can run.
Is Firefox 156 still safe?
Not any more. The 6 updates since, up to Firefox 159.0.1, fix 325 security flaws that Firefox 156 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 73 security flaws, 0 rated critical and 27 high by Mozilla.[1] The 27 critical and high ones are:
| Flaw | Severity | What Mozilla calls it |
|---|---|---|
CVE-2026-92005 | High | Use-after-free in the Audio/Video: Web Codecs component |
CVE-2026-92006 | High | Privilege escalation due to incorrect boundary conditions in the Graphics: CanvasWebGL component |
CVE-2026-92007 | High | Privilege escalation due to incorrect boundary conditions in the Graphics: CanvasWebGL component |
CVE-2026-92008 | High | Privilege escalation due to incorrect boundary conditions in the Graphics: CanvasWebGL component |
CVE-2026-92009 | High | Privilege escalation due to incorrect boundary conditions in the Graphics: CanvasWebGL component |
CVE-2026-92010 | High | Privilege escalation due to incorrect boundary conditions in the Graphics: CanvasWebGL component |
CVE-2026-92011 | High | Privilege escalation due to incorrect boundary conditions in the Graphics: CanvasWebGL component |
CVE-2026-92012 | High | Privilege escalation due to incorrect boundary conditions in the Graphics: CanvasWebGL component |
CVE-2026-92013 | High | Privilege escalation due to incorrect boundary conditions in the Graphics: CanvasWebGL component |
CVE-2026-92015 | High | Privilege escalation in the WebExtensions component |
CVE-2026-92034 | High | Site isolation issue in the Graphics component |
CVE-2026-92035 | High | Sandbox escape due to incorrect boundary conditions in the Graphics component |
CVE-2026-92016 | High | Use-after-free in the Disability Access APIs component |
CVE-2026-92017 | High | Privilege escalation in the DOM: Service Workers component |
CVE-2026-92018 | High | Sandbox escape in the DOM: Core & HTML component |
CVE-2026-92020 | High | Privilege escalation due to incorrect boundary conditions in the Graphics: WebRender component |
CVE-2026-92022 | High | Use-after-free in the DOM: HTML Parser component |
CVE-2026-92023 | High | Use-after-free in the XML component |
CVE-2026-92024 | High | Use-after-free in the SVG component |
CVE-2026-92025 | High | Use-after-free in the DOM: Navigation component |
CVE-2026-92026 | High | Use-after-free in the Networking component |
CVE-2026-92036 | High | Incorrect boundary conditions in the Networking: HTTP component |
CVE-2026-92027 | High | Use-after-free in the DOM: Streams component |
CVE-2026-92028 | High | Use-after-free in the DOM: Core & HTML component |
CVE-2026-92029 | High | Use-after-free in the SVG component |
CVE-2026-92037 | High | Incorrect boundary conditions in the DOM: Animation component |
CVE-2026-92038 | High | Mitigation bypass in the Remote Settings Client 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 157 or later.
155 vs 156
Firefox 155, released 1 Sep 2026, fixed 29 security flaws. Firefox 156 fixes 73 security flaws and includes the fixes before it, so going straight to 156 gets you both.
- Before: Firefox 155, 1 Sep 2026, 29 security flaws
- After: Firefox 157, 29 Sep 2026, 76 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 156”, 15 Sep 2026.