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Should you update to Firefox 159.0.1?

From Firefox updates, in the HARD wiki · Updated
This article is about one Firefox release. For the latest version, see Firefox updates.

Yes, soon. Firefox 159.0.1 is a security update Mozilla released on 3 Nov 2026 for Mac, Windows and Linux. It fixes 1 security flaw, 0 rated critical and 1 high by Mozilla.[1] None of them is known to be used in attacks.

It is the newest Firefox release, so it’s the one to have.

Should you update?

Yes, soon. None of its fixes is known to be used in attacks yet. Automatic updates will install it for you. 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 159.0.1 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 (☰ menu → Help → About Firefox).

What it fixes

Mozilla lists 1 security flaw, 0 rated critical and 1 high by Mozilla.[1] The critical or high one is:

FlawSeverityWhat Mozilla calls it
CVE-2026-120572HighIncorrect boundary conditions in the Layout: Block and Inline component

How to update, and how long it takes

A minute or two. Firefox restarts and reopens your tabs.

  1. Open Firefox’s About window.Open the ☰ menu → Help → About Firefox. Firefox checks for the update and downloads it.
  2. Click Restart to update Firefox.Firefox reopens your windows and tabs. Until it restarts, the old, unfixed version keeps running.
  3. 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 159.0.1 or later.

159 vs 159.0.1

Firefox 159, released 27 Oct 2026, fixed 167 security flaws. Firefox 159.0.1 fixes 1 security flaw and includes the fixes before it, so going straight to 159.0.1 gets you both.

  • Before: Firefox 159, 27 Oct 2026, 167 security flaws
  • After: none yet. This is the newest.
  • Firefox updates, every release and the latest version
  • Updates, the latest version of everything HARD tracks

References

  1. ^ Mozilla. “Security Vulnerabilities fixed in Firefox 159.0.1”, 3 Nov 2026.