See what landed recently in Firefox Nightly!

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.

140.0a1 Firefox Nightly

April 28, 2025

Version 140.0a1, first offered to Nightly channel users on April 28, 2025

Firefox Nightly gets updated every day and as a consequence, the release notes for the Nightly channel are updated continuously to reflect features that have reached sufficient maturity to benefit from community feedback and bug reports.

Warning: Features listed here may or may not make a final release of Firefox.

In addition to these release notes, you can follow ongoing development on our @FirefoxNightly Bluesky account, our @FirefoxNightly Mastodon account as well as read our Nightly Blog.

You can interact with other Firefox Nightly users and give your feedback to Mozilla staff in the Nightly Matrix room on chat.mozilla.org.

New

  • Starting with Firefox 139, Smart Tab Groups is now available in Nightly builds, enhancing the creation of new groups by automating the process of grouping semantically similar tabs and labeling the group.

    Bug 1955779

Developer

Web Platform

  • Starting with Firefox 138, H265 decoding for WebCodecs is now enabled for Nightly Linux builds.

    Bug 1949917

  • Starting with Firefox 137, H265 decoding for WebCodecs is now enabled for Nightly MacOS builds.

    Bug 1944991

  • Starting with Firefox 139, Nightly builds now support PerformanceEventTiming.interactionId, allowing developers to group related input events. This enables support for the Interaction to Next Paint (INP) responsiveness metric.

    Bug 1957012

  • Starting with Firefox 139, Nightly builds no longer dispatch the non-standard afterscriptexecute and beforescriptexecute events.

    Bug 1954685

  • Starting with Firefox 139, Nightly builds now support the View Transition API.

    Bug 1950759

Get the most recent version

All Firefox Nightly downloads