Should you update to Firefox 157?
No: install Firefox 159.0.1 instead. Firefox 157 is a security update Mozilla released on 29 Sep 2026 for Mac, Windows and Linux. It fixes 76 security flaws, 0 rated critical and 38 high by Mozilla.[1] None of them is known to be used in attacks.
It has since been replaced by Firefox 157.0.1, released 6 Oct 2026, which includes all of its fixes.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 157, so there’s no reason to stop at this one. Software Update offers the newest version your device can run.
Is Firefox 157 still safe?
Not any more. The 5 updates since, up to Firefox 159.0.1, fix 249 security flaws that Firefox 157 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 76 security flaws, 0 rated critical and 38 high by Mozilla.[1] The 38 critical and high ones are:
| Flaw | Severity | What Mozilla calls it |
|---|---|---|
CVE-2026-100756 | High | Incorrect boundary conditions in the Audio/Video: Playback component |
CVE-2026-100757 | High | Use-after-free in the Widget component |
CVE-2026-100758 | High | Sandbox escape in the DOM: Navigation component |
CVE-2026-100759 | High | Uninitialized memory in the Storage: Quota Manager component |
CVE-2026-100760 | High | Sandbox escape in the Security: Process Sandboxing component |
CVE-2026-100761 | High | Privilege escalation due to use-after-free in the Graphics: WebGPU component |
CVE-2026-100762 | High | Sandbox escape due to use-after-free in the DOM: Content Processes component |
CVE-2026-100763 | High | Incorrect boundary conditions in the Graphics: WebGPU component |
CVE-2026-100764 | High | Privilege escalation due to incorrect boundary conditions in the Graphics: WebGPU component |
CVE-2026-100765 | High | Use-after-free in the JavaScript: WebAssembly component |
CVE-2026-100766 | High | Information disclosure in the Networking: JAR component |
CVE-2026-100767 | High | Use-after-free in the Networking: Cache component |
CVE-2026-100768 | High | Use-after-free in the Graphics: WebGPU component |
CVE-2026-100769 | High | Use-after-free in the JavaScript: WebAssembly component |
CVE-2026-100770 | High | Sandbox escape due to use-after-free in the DOM: Content Processes component |
CVE-2026-100771 | High | Undefined behavior in the DOM: Streams component |
CVE-2026-100772 | High | Use-after-free in the DOM: Core & HTML component |
CVE-2026-100773 | High | Use-after-free in the Storage: IndexedDB component |
CVE-2026-100774 | High | Use-after-free in the DOM: Core & HTML component |
CVE-2026-100775 | High | Sandbox escape in the Graphics component |
CVE-2026-100776 | High | Use-after-free in the JavaScript: WebAssembly component |
CVE-2026-100777 | High | Use-after-free in the Graphics: Canvas2D component |
CVE-2026-100778 | High | Sandbox escape due to use-after-free in the DOM: Core & HTML component |
CVE-2026-100779 | High | Use-after-free in the XSLT component |
CVE-2026-100780 | High | Use-after-free in the DOM: Core & HTML component |
CVE-2026-100781 | High | Sandbox escape due to incorrect boundary conditions in the Graphics: WebRender component |
CVE-2026-100782 | High | Privilege escalation due to incorrect boundary conditions in the Graphics component |
CVE-2026-100783 | High | Uninitialized memory in the Audio/Video component |
CVE-2026-100784 | High | Use-after-free in the Layout: Text and Fonts component |
CVE-2026-100785 | High | Use-after-free in the DOM: Core & HTML component |
| and 8 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. 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 157.0.1 or later.
156 vs 157
Firefox 156, released 15 Sep 2026, fixed 73 security flaws. Firefox 157 fixes 76 security flaws and includes the fixes before it, so going straight to 157 gets you both.
- Before: Firefox 156, 15 Sep 2026, 73 security flaws
- After: Firefox 157.0.1, 6 Oct 2026, 1 security flaw
- Firefox updates, every release and the latest version
- Updates, the latest version of everything HARD tracks
References
- ^ Mozilla. “Security Vulnerabilities fixed in Firefox 157”, 29 Sep 2026.