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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.

129.0a1 Firefox Nightly

June 10, 2024

Version 129.0a1, first offered to Nightly channel users on June 10, 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 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
  • Starting with Firefox 128, hovering the mouse over an unfocused tab will now display a visual preview of its contents in Nightly builds.

    Bug 1893676
  • Added support for multiple languages in the same document spoken in macOS VoiceOver.

    Bug 1678712
  • Starting with Firefox 129, Firefox Nightly blocks third-party cookie access with Enhanced Tracking Protection's Strict mode and also in Private Browsing.

    Bug 1898255
  • Starting with Firefox 129, Firefox Nightly will automatically try to use a secure HTTPS connection whenever possible when loading a page. This behavior is known as "HTTPS-First", or "HTTPS Upgrades", and has been the default in Firefox's private browsing mode since Firefox 91. Here is a blog post from when this feature was introduced in Private Browsing.

    Bug 1719271

Web Platform

  • 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
  • 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
  • Starting with Firefox 128, Firefox Nightly now has initial support for the CHIPS (Cookies Having Independent Partitioned State) standard.

    Bug 1898253
  • Added support for querying the encryption key system config in mediaCapabilities.decodingInfo() API

    Bug 1898344
  • Added support for Float16Array typed arrays along with new DataView methods for reading and setting Float16 values, and a Math.f16round() static method that can be used to round numbers to 16 bits. The new type is useful for sharing data with a GPU, in particular for use cases where it makes sense to trade off precision for memory consumption.

    Bug 1903329

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