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.

145.0a1 Firefox Nightly

September 15, 2025

Version 145.0a1, first offered to Nightly channel users on September 15, 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 143, Firefox Nightly now blocks local network requests by default and only allows them if the user grants access through a permission prompt, strengthening protection against attacks targeting local network services.

    Bug 1972350

  • Starting with Firefox 145, it is now possible to add comments in the Firefox PDF viewer.

    Bug 1987149

Changed

  • Starting with Firefox 145, 32-bit Linux is no longer supported. We encourage users to install a 64-bit version of Firefox.

    Bug 1987132

  • Horizontal tabs are now slightly more round, following the look of vertical tabs. Buttons and text inputs, including the Address bar, have been updated as well for consistency.

    Bug 1988794

Developer

Web Platform

  • Starting with Firefox 144, layer compositor is enabled for WebRender on Windows in Firefox Nightly.

    Bug 1945683

  • Support has been added for the Atomics.waitAsync proposal, which is a non-blocking, asynchronous version of Atomics.wait. This allow synchronization of threads based upon the value in a shared memory location, for more details please consult our MDN documentation.

    Bug 1884148

  • Starting with Firefox 145, the text-autospace property is supported, allowing automatic spacing adjustments between characters from different scripts.

    Bug 1988596

  • Starting with Firefox 145, we now support the legacy -webkit-fill-available keyword as a value for the CSS width and height properties, to improve rendering of content on the web that uses this keyword. This keyword is an alias for the recently standardized stretch keyword (which isn't shipping in Firefox yet).

    Bug 1988938

  • Starting with Firefox 145, support has been added for CSS module scripts, disabled by default using the preference layout.css.module-scripts.enabled. CSS module scripts allow for CSS scripts to be imported like ECMAScript modules using import attributes.

    Bug 1720570

  • Starting with Firefox 145, Nightly builds now support CSS anchor positioning, which allows to tether elements together. The anchor-positioned elements can then have their size and position set relative to the size and location of the anchor elements to which they are bound.

    Bug 1988224

  • Firefox now partially supports the new Integrity-Policy header, which is used to enforce sub-resource integrity for scripts.

    Bug 1984973

  • Starting with Firefox 145, the Trusted Types API, primarily aimed at preventing cross-site scripting attacks, is now enabled in Nightly.

    Bug 1955251

  • Added Matroska support for the most commonly used codecs: AVC, HEVC, VP8, VP9, AV1, AAC, Opus, and Vorbis.

    Bug 1991752

Get the most recent version

All Firefox Nightly downloads