Firefox Release Notes

Release Notes tell you what’s new in Firefox. As always, we welcome your feedback. You can also file a bug in Bugzilla or see the system requirements of this release.

Firefox Release

March 19, 2019

Version 66.0, first offered to Release channel users on March 19, 2019

We'd like to extend a special thank you to all of the new Mozillians who contributed to this release of Firefox!



  • The Dark and Light Firefox themes now override the system setting for title bar accent color on Windows 10

  • Linux users: Resolved an issue that caused Firefox to freeze when downloading files

  • Various security fixes


  • System title bar is hidden by default to match Gnome guideline for Linux users


  • Developer Information
  • DevTools Inspector is now fully usable when the Debugger is paused

  • Lowered priority of setTimeout and setInterval during page load to improve overall page load performance

  • Fixed: <button> element is no longer special cased in event dispatch, per latest specifications

All Firefox downloads