Should you update to Firefox ESR 153.6?
Yes, this week. Firefox ESR 153.6 is a security update Mozilla released on 27 Oct 2026 for Mac, Windows and Linux, mostly in workplaces and schools. It fixes 145 security flaws, 0 rated critical and 95 high by Mozilla.[1] None of them is known to be used in attacks.
It is the newest Firefox ESR 153 release, so it’s the one to have.
Should you update?
Yes, this week. It fixes 145 security flaws, and attackers study each release to work out what it fixed. Every security update closes holes that become public the moment it ships, so the risk of staying on the old version only grows. Waiting a week to see if others hit problems is a common habit; with a security update it’s the wrong trade.
Is Firefox ESR 153.6 safe to install?
Yes. It’s Mozilla’s own security release, and updates rarely go wrong; a backup makes it painless if one does. The one unsafe way to get it is from a link: Mozilla never sends updates by email, text or pop-up, so install it only from Firefox’s own About window, or your IT team.
What it fixes
Mozilla lists 145 security flaws, 0 rated critical and 95 high by Mozilla.[1] The 95 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-2026-117874 | 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-2026-117877 | High | Use-after-free in the Layout: Text and Fonts 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-2026-117880 | High | Use-after-free in the XML 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 |
CVE-2026-117885 | High | Use-after-free in the Layout: Grid component |
CVE-2026-117886 | High | Incorrect boundary conditions in the Graphics: Text component |
CVE-2026-117887 | High | Use-after-free in the DOM: Core & HTML component |
CVE-2026-117888 | High | Uninitialized memory in the Graphics: Canvas2D component |
CVE-2026-117889 | High | Incorrect boundary conditions in the JavaScript Engine component |
| and 65 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. 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 153.6 or later.
Older devices
The same day, Mozilla released Firefox ESR 115.44 (80 security flaws) for devices that stay on an older version. Each fixes the same holes where they apply.
153.5.1 vs 153.6
Firefox ESR 153.5.1, released 20 Oct 2026, fixed 1 security flaw. Firefox ESR 153.6 fixes 145 security flaws and includes the fixes before it, so going straight to 153.6 gets you both.
- Before: Firefox ESR 153.5.1, 20 Oct 2026, 1 security flaw
- After: none yet. This is the newest.
- 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 153.6”, 27 Oct 2026.