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Firefox Nightly
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.

127.0a1 Firefox Nightly

April 15, 2024

Version 127.0a1, first offered to Nightly channel users on April 15, 2024

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 Twitter account, our 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


  • Starting with Firefox 124, a simpler and more unified dialog for clearing user data is now available in Nightly builds. In addition to streamlining data categories, the new dialog also provides insights into the site data size corresponding to the selected time range.

    Bug 1874702
  • Starting with Firefox 125, Nightly builds support resolving HTTPS DNS records with the operating system's DNS resolver on specific platforms (Windows 11, Linux, Android 10+) without requiring DNS over HTTPS to be enabled. This capability allows the use of HTTP/3 without needing to use the Alt-Svc header, upgrades requests to HTTPS when the DNS record is present, and enables wider use of ECH. This feature is expected to ship in Firefox 126.

    Bug 1874464
  • You can now set Firefox to automatically launch whenever you start or restart your Windows computer. Setting Firefox to auto-launch optimizes efficiency in our browser-centric digital routines, eliminating manual startup delays and facilitating immediate web access. (Learn more)

    Bug 1892782
  • We completed work to optimize and enable DNS prefetching for HTTPS documents via the rel="dns-prefetch" link hint. This standard allows web developers to specify domain names for important assets that should be resolved preemptively.

    Bug 1596935
  • Starting with Firefox 127, we're enabling a new anti-tracking feature in Nightly: Bounce Tracking Protection. This protection detects bounce trackers based on redirect behavior and periodically purges their cookies & site data to prevent tracking.

    Bug 1895222
  • It is now possible to close all duplicate tabs in a window with the Close duplicate tabs command available from the List all tabs widget in the tab bar or a tab context menu.

    Bug 1892659


  • To reduce user fingerprinting information and the risk of some website compatibility issues, the CPU architecture for 32-bit x86 Linux will now be reported as x86_64 in Firefox's User-Agent string and navigator.platform and navigator.oscpu Web APIs.

    Bug 1873273
  • Links and other focusable elements are now tab-navigable by default on macOS, instead of following macOS' "Keyboard navigation" setting. This is a more accessible default and matches the default in all other platforms. A checkbox in the settings page still allows users to restore the old behavior.

    Bug 1036966
  • The Screenshots feature in Firefox has gotten a big update! It now supports taking screenshots of file types like SVG, XML, and more as well as various about: pages within Firefox. We've also made the screenshot tool more accessible to everyone by implementing new keyboard shortcuts and adding theme compatibility and High Contrast Mode (HCM) support. And finally, performance for capturing large screenshots has been improved.

    Bug 1870127

Web Platform

  • Starting with Firefox 125, the transition-behavior CSS property is now supported in Nightly builds.

    Bug 1805727
  • Starting with Firefox 125, Nightly builds will attempt to establish TLS connections using a hybrid post-quantum key agreement mechanism (X25519+Kyber768). This may result in slow TLS handshakes or failed connections on networks with TLS intercepting middleboxes. The feature can be disabled by setting the security.tls.enable_kyber preference to false.

    Bug 1878725
  • Starting with Firefox 126, the shape() function on clip-path property is now supported in nightly builds.

    Bug 1823463
  • Starting with Firefox 126, the shape() function on offset-path property is supported in nightly builds.

    Bug 1884424
  • Starting with Firefox 126, interpolation between path() function and shape() function is now supported in nightly builds.

    Bug 1884425
  • Starting with Firefox 127, Nightly users now have the ability to translate selections of text from the right-click context menu, rather than only being able to translate the entire web page.

    Bug 1890299
  • Starting with Firefox 127, the relative color syntax is supported in CSS color functions in Nightly builds. This allows to create colors based on other colors.

    Bug 1893965
  • has been enabled (see documentation). A paste context menu will appear for the user to confirm when attempting to read clipboard content that is not originated from a same-origin page.

    Bug 1887845
  • Added support for the new Set JavaScript methods for creating unions and intersections of two sets.

    Bug 1868423
  • Starting with Firefox 127, @starting-style is supported in Nightly builds. This at-rule allows to define styles that are applied to an element when it is first rendered, enabling transitions on elements that are added to the DOM or that have their display type changed from none to another value.

    Bug 1834876

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