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.

139.0a1 Firefox Nightly

March 31, 2025

Version 139.0a1, first offered to Nightly channel users on March 31, 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 136, profile management is now available in Nightly builds. Users can now more easily create and switch between different profiles.

    Bug 1931006

  • Starting with Firefox 137, you can now you can easily add your signatures to PDFs. Draw, type, or upload your signature, then place it exactly where you want. Save your go-to signatures for next time.

    Bug 1948482

Developer

Web Platform

  • Starting with Firefox 136, scroll-driven animations is enabled in Nightly builds.

    Bug 1817303

  • Starting with Firefox 137, the Temporal proposal is enabled by default in Firefox Nightly, please experiment with it and provide feedback. Temporal is a better version of Date, for more details, please see https://tc39.es/proposal-temporal/docs/.

    Bug 1946823

  • 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

  • window.getSelection().toString() now correctly returns the text serialization when text is selected in a text control, improving cross-browser interoperability on some sites.

    Bug 1954979

  • 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 hidden=until-found attribute, allowing content to be found via find-in-page when it's otherwise hidden by default.

    Bug 1761043

  • Closed <details> elements are now searchable and can be automatically expanded if found via find-in-page.

    Bug 1724299

Get the most recent version

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