Should you update to Firefox 154?
No: install Firefox 159.0.1 instead. Firefox 154 is a security update Mozilla released on 18 Aug 2026 for Mac, Windows and Linux. It fixes 58 security flaws, 0 rated critical and 16 high by Mozilla.[1] None of them is known to be used in attacks.
It has since been replaced by Firefox 155, released 1 Sep 2026, which includes all of its fixes.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 154, so there’s no reason to stop at this one. Software Update offers the newest version your device can run.
Is Firefox 154 still safe?
Not any more. The 8 updates since, up to Firefox 159.0.1, fix 427 security flaws that Firefox 154 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 58 security flaws, 0 rated critical and 16 high by Mozilla.[1] The 16 critical and high ones are:
| Flaw | Severity | What Mozilla calls it |
|---|---|---|
CVE-2026-75874 | High | Sandbox escape in the Remote Settings Client component |
CVE-2026-74934 | High | Site isolation issue in the Graphics: CanvasWebGL component |
CVE-2026-74935 | High | Privilege escalation in the DOM: Networking component |
CVE-2026-74936 | High | Use-after-free in the JavaScript: WebAssembly component |
CVE-2026-74937 | High | Use-after-free in the JavaScript: GC component |
CVE-2026-74938 | High | Mitigation bypass in the JavaScript: GC component |
CVE-2026-74939 | High | Privilege escalation in the DOM: Navigation component |
CVE-2026-74941 | High | Privilege escalation in the Graphics: CanvasWebGL component |
CVE-2026-74943 | High | Use-after-free in the Graphics: ImageLib component |
CVE-2026-74944 | High | Use-after-free in the DOM: Core & HTML component |
CVE-2026-74945 | High | Information disclosure in the Graphics: Text component |
CVE-2026-74947 | High | Privilege escalation due to invalid pointer in the Graphics component |
CVE-2026-74948 | High | Information disclosure in the Graphics component |
CVE-2026-74987 | High | Internally found bugs fixed in Firefox ESR 140.14, Firefox ESR 153.1 and Firefox 154 |
CVE-2026-74988 | High | Internally found bugs fixed in Firefox ESR 153.1 and Firefox 154 |
CVE-2026-74990 | High | Internally found bugs fixed in Firefox ESR 115.39, Firefox ESR 140.14, Firefox ESR 153.1 and Firefox 154 |
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 155 or later.
153 vs 154
Firefox 153, released 21 Jul 2026, fixed 63 security flaws. Firefox 154 fixes 58 security flaws and includes the fixes before it, so going straight to 154 gets you both.
- Before: Firefox 153, 21 Jul 2026, 63 security flaws
- After: Firefox 155, 1 Sep 2026, 29 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 154”, 18 Aug 2026.