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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.

125.0a1 Firefox Nightly

February 19, 2024

Version 125.0a1, first offered to Nightly channel users on February 19, 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
  • Firefox now prompts users in the US and Canada to save their addresses upon submitting an address form, allowing Firefox to autofill stored address information in the future.

    Bug 1875254
  • Firefox has expanded its download protection and now more proactively blocks downloads from URLs that are considered to be potentially untrustworthy.

    Bug 1877195
  • The URL Paste Suggestion feature provides a convenient way for users to quickly visit URLs copied to the clipboard in the address bar of Firefox. When the clipboard contains a URL and the URL bar is focused, an autocomplete result appears automatically. Activating the clipboard suggestion will navigate the user to the URL with 1 click.

    Bug 1882478
  • Firefox now provides an option to enable Web Proxy Auto-Discovery (WPAD) while configured to use system proxy settings.

    Bug 621429
  • Users of tab-specific Container add-ons can now search in the Address Bar for tabs that are open in different containers. Special thanks to volunteer contributor atararx for kicking off the work on this feature!

    Bug 1882815
  • It is now possible to highlight in PDFs.

    Bug 1867513

    This feature is part of a progressive roll out.

    What is a progressive roll out?

    Certain new Firefox features are released gradually. This means some users will see the feature before everyone does. This approach helps to get early feedback to catch bugs and improve behavior quickly, meaning more Firefox users overall have a better experience.

  • 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


  • In a group of radio buttons where no option is selected, the tab key now only reaches the first option, rather than every option being reachable with tab. The arrow keys navigate between options as they do when there is a selected option. This makes keyboard navigation more efficient and consistent.

    Bug 1267488
  • Firefox for Android no longer includes the variant and extension of BCP47 in the Accept-Language header of HTTP requests for better interoperability with other browsers.

    Bug 1847701

Web Platform

  • Added support for the content-box and stroke-box keywords of the transform-box CSS property.

    Bug 1868374
  • Support for SVGAElement.text was removed in favor of the more widely-implemented SVGAElement.textContent method.

    Bug 1880689
  • Starting with Firefox 125, the transition-behavior CSS property is now supported in Nightly builds.

    Bug 1805727
  • The popover global attribute is used to designate an element as a popover element. The element won't render until it becomes shown, it will then render on top of other page content.

    Bug 1866993
  • align-content works now in block layout, allowing block direction alignment without needing a flex or grid container.

    Bug 1684236
  • Enabled WebAssembly multi-memory by default. Wasm multi-memory allows wasm modules to use and import multiple independent linear memories. This enables more efficient interop between modules, and better polyfills for upcoming wasm standards like the component model.

    Bug 1860816
  • 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 124, Nightly builds include support for the Screen Wake Lock API.

    Bug 1874849
  • Added support for Unicode text segmentation to JavaScript.

    Bug 1883914


  • Some macOS Nightly users may see a prompt like the one below when trying to update a more recent build:

    Screenshot of macOS reinstall prompt

    While the underlying cause of this bug was identified and resolved, users in this state should follow the instructions from the prompt and manually reinstall. No data will be lost in the process and this should only need to be done once for automatic updates to resume.

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