Version 154.0a1, first offered to Nightly channel users on June 15, 2026
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.
Starting with Firefox 152, the address bar in Nightly builds autofills the pages you visit most - including specific pages within a site, not just site homepages - based on your browsing habits, and lets you dismiss suggestions you don’t want.
Exceptions for sites that have their cookies & site data cleared on shutdown can now be set without exempting the site from tracking protection and other cookie restrictions.
Starting with Firefox 154, Firefox Nightly now supports QUIC version 2 (RFC 9369) for HTTP/3 connections. Firefox offers both QUIC v1 and v2 using compatible version negotiation (RFC 9368). The server selects which version is used, so connections upgrade to QUIC v2 when the server chooses it and remain on QUIC v1 otherwise.
Firefox's Local Network Access protections now extends to WebSocket connections. Websites that try to open a WebSocket to a device on your local network will now ask for your permission first
In Firefox for Android, improved the reliability of automatic translations for users with multiple languages selected in system settings.
The address bar now includes a "Manage AI" quick action that opens the AI section of Settings.
Video seeking is now significantly faster on macOS, making scrubbing and jumping to a point in a video much more responsive.
The JSON Viewer now shows a breadcrumb path at the bottom for the selected entry.
Firefox now supports Iterator.prototype.includes(), allowing developers to check whether an iterator contains a given value without first converting it to an array.
Starting with Firefox 152, Nightly builds allow the attr() function to be used in any CSS property. It now also allows to specify how the attribute value is parsed into a CSS value.
Starting with Firefox 154, Firefox Nightly now supports the alpha() CSS function. This is a relative color function that can be used to modify just the alpha component of a given color.
Starting with Firefox 153, Firefox Nightly ships an experimental implementation of the link-parameters property by Tyler Thrailkill.
Added a time picker user interface to <input type="time"> and <input type="datetime-local">, making selecting a time more accessible and intuitive.
Starting with Firefox 154, Firefox Nightly now supports the progress() CSS function. This is a math function that can be used in calculations to compute the position of a value relative to a start and an end.
Starting with Firefox 153, Nightly builds support the new JPEG XL image format, which generally has better compression than WebP, JPEG, PNG and GIF and is designed to supersede them.
Starting with Firefox 153, Firefox Nightly now supports two new keywords closest-corner and farthest-corner for the radial size in the circle() and ellipse() functions.
Firefox now supports the sibling-index() and sibling-count() CSS functions. These functions allow an element to be styled with calculations that use its index among its siblings and its total count of siblings (including itself), respectively.
Starting with Firefox 154, Firefox Nightly now supports the text-box-trim and text-box-edge CSS properties, and the associated text-box shorthand. These properties allow you to control the leading space above and below text, enabling simpler and consistent vertical spacing and alignment.
Firefox now supports the Iterator.prototype.join method that allows joining an iterator into a string, similar to Array.prototype.join.
Starting with Firefox 154, Firefox Nightly now supports the CSS Typed Object Model API (Typed OM). This API allows web applications and other Web Platform features to work with CSS values through typed JavaScript objects instead of strings.
Added support for the No-Vary-Search HTTP response header for the HTTP disk cache. Servers can now declare which URL query parameters are irrelevant to the response, allowing Firefox to reuse cached resources across parameter variations and improving cache hit rates.
Firefox now supports new Iterator.prototype.chunks and Iterator.prototype.windows methods that allow consuming an iterator as either overlapping or non-overlapping subsequences of configurable size.
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