Mozilla first offered Firefox 159.0 to Release-channel users on October 27, 2026, alongside Security Advisory 2026-118, which Mozilla rates as high impact overall. Malwarebytes reports that the update addresses 167 vulnerabilities; individual entries in Mozilla’s advisory are rated high, moderate, or low.

What the security advisory says

Mozilla’s advisory describes issues including use-after-free bugs, sandbox escapes, same-origin policy bypasses, privilege escalation, and information disclosure. These are examples of individual vulnerability types, not one description of every issue. Mozilla names OpenAI Codex Security (kylebot) and Amy Burnett of OpenAI as reporters on some entries.

What changes in Firefox 159

Firefox 159 adds a native macOS sharing panel, with page previews and recent contacts; you can also share multiple selected tabs. Saved passwords are available from the sidebar by default.

Smart Window can monitor a page for changes such as price drops or restocks. Type /watch in the chat to set up a watch. Firefox can send desktop notifications, and you can manage watches from the toolbar’s Tasks button or about:smartwindowtasks. Mozilla is rolling Smart Window out progressively, so it may not appear for everyone at the same time.

The release also changes keyboard shortcuts. Open-tab search uses Ctrl+Shift+A on Windows and Linux, or Cmd+Shift+A on macOS. Extensions and Themes uses Ctrl+Shift+F on Windows and Linux, or Cmd+Shift+E on macOS. You can change shortcuts in about:keyboard.

Fixes and how to check for the update

Mozilla lists several fixes tied to specific conditions:

  • Reduced rapid memory growth when minimized web apps such as Zoom remain open.
  • Addressed excessive memory use on Linux with AMD graphics while viewing map or place results on sites such as ChatGPT.
  • Fixed some Windows video-rendering issues involving NVIDIA RTX Video HDR.
  • Improved fallback to HTTP/2 on sites such as Slack when they reject HTTP/3.
  • Fixed a problem importing bookmarks from Google Chrome profiles signed in to a Google account.

To check for Firefox 159.0, open the Firefox menu and select Help > About Firefox. Let Firefox check for and download an available update, then relaunch the browser if prompted.