Should you update to Firefox ESR 153.3?
No: install Firefox ESR 153.6 instead. Firefox ESR 153.3 is a security update Mozilla released on 15 Sep 2026 for Mac, Windows and Linux, mostly in workplaces and schools. It fixes 63 security flaws, 0 rated critical and 24 high by Mozilla.[1] None of them is known to be used in attacks.
It has since been replaced by Firefox ESR 153.4, released 29 Sep 2026, which includes all of its fixes.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 ESR 153.6 instead. Firefox ESR 153.6 came out on 27 Oct 2026 and includes every fix in Firefox ESR 153.3, so there’s no reason to stop at this one. Software Update offers the newest version your device can run.
Is Firefox ESR 153.3 still safe?
Not any more. The 4 updates since, up to Firefox ESR 153.6, fix 268 security flaws that Firefox ESR 153.3 doesn’t, and each became public the day its fix shipped. Installing it is safe: get it only from Firefox’s own About window, or your IT team, never from a link in an email, text or pop-up.
What it fixes
Mozilla lists 63 security flaws, 0 rated critical and 24 high by Mozilla.[1] The 24 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-2026-92035 | 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-2026-92027 | 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-2026-92038 | 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. If your workplace or school manages Firefox, its IT team may install ESR updates for you.
- Click Restart to update Firefox.Firefox reopens your windows and tabs. Until it restarts, the old, unfixed version keeps running.
To check it worked: The ☰ menu → Help → About Firefox shows the version, ending in esr. It should say 153.4 or later.
Older devices
The same day, Mozilla released Firefox ESR 140.16 (28 security flaws) and Firefox ESR 115.41 (21 security flaws) for devices that stay on an older version. Each fixes the same holes where they apply.
153.2 vs 153.3
Firefox ESR 153.2, released 1 Sep 2026, fixed 24 security flaws. Firefox ESR 153.3 fixes 63 security flaws and includes the fixes before it, so going straight to 153.3 gets you both.
- Before: Firefox ESR 153.2, 1 Sep 2026, 24 security flaws
- After: Firefox ESR 153.4, 29 Sep 2026, 62 security flaws
- Firefox ESR updates, every release and the latest version
- Updates, the latest version of everything HARD tracks
References
- ^ Mozilla. “Security Vulnerabilities fixed in Firefox ESR 153.3”, 15 Sep 2026.