October 27, 2026. Firefox 159 has reached the desktop Release channel, and Mozilla has published a security advisory identifying vulnerabilities fixed in that version.
The October 27 advisory, MFSA 2026-118, carries an overall high-impact rating. Its entries include same-origin policy bypass, sandbox escape and memory-safety issues. This article does not claim that any listed flaw is being actively exploited.
Check the version you are actually running
Use Firefox’s built-in About or update interface to check the installed version and complete any requested restart. If your installation is managed by an employer or supplied through your operating system’s package manager, follow that update channel rather than installing an unrelated build over it.
The release notes also describe interface changes, including native sharing on macOS and saved passwords appearing in the sidebar by default. New-feature availability is not a reliable test of whether every security update has been applied.
Match the advisory to your product
The advisory names Firefox and version 159. Do not assume that a desktop version number describes Firefox for Android, iOS or an Extended Support Release installation. Check the advisory and update instructions for the product you actually use.
Keep the download path ordinary: the browser’s updater, your organization’s software service or the official vendor site. A web page urging you to paste a repair command is not a substitute for an update.
Photo: Leone Venter / Unsplash, Unsplash License. Illustrative stock photograph.
