Version 151.0a1, first offered to Nightly channel users on March 23, 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 149, Nightly builds now ship with a new .rpm package for Linux users on Red Hat, Fedora, openSUSE, and other RPM-based distributions.
Starting with Firefox for Android 150, Nightly users can now choose a custom default location for their downloads.
On macOS, URLs copied from iOS devices using Apple’s Universal Clipboard now paste correctly in Firefox.
HTML <select> dropdowns now display as an OS-native menu on macOS, aligning their appearance and behavior with the rest of the system.
The about:translations page is now accessible through the More Tools section of the Application Menu.
Starting with Firefox 151, Firefox for Android nightly builds include settings for enabling fine-grained control of AI features and also allows you to block future AI features.
Starting with Firefox 151, you can merge multiple PDFs within the Firefox PDF viewer in Nightly builds.
Address Autofill is enabled for users in the Netherlands.
With Firefox for Android you can now to swipe vertically over the toolbar to quickly see your list of tabs.
Private Browsing Mode now has a new privacy feature that allows users to instantly clear all data from their current private session without closing the entire browser.
Standard Enhanced Tracking Protection mode is getting increased protections against fingerprinting that limit the amount of information revealed about your computer and frustrating attempts to track you across websites.
Correct screen resolution reporting via JS APIs in multiple monitor setups.
Improved color management for copied and pasted images on macOS.
Fixed an issue on macOS where maximized Firefox windows could reopen on the wrong monitor after relaunching in multi-display setups.
The search bar in Firefox Settings (about:preferences) is now larger and spans the full Settings column, making it easier for users to search within Settings.
Geolocation on Windows now respects the user's Windows location permission setting, instead of overriding it, when the user grants location permission to a page. Firefox will ask users to enable the Windows permission if it is needed.
Extensions and Themes installed in a Firefox Desktop profile directory will be restored successfully after the profile directory is moved (or restored) to a different location or a different operating system.
Starting with Firefox 151, the JavaScript Tracer can be enabled from DevTools Settings panel in Nightly builds. This enables tracing all JavaScript function calls. Unlike the performance profiler, this doesn't record a sample; instead, it traces all function calls.
Starting with Firefox 149, you can now set specific color spaces and transparency (alpha) on <input type="color"> elements, with alpha support currently exclusive to Firefox Nightly. While the visual picker hasn't changed yet (tracked in Bug 2007532), it will now output values in your requested format.
Starting with Firefox 149, Nightly builds now support throttling for Web Workers running in inactive tabs. When a tab becomes inactive, Firefox reduces how aggressively its workers can run timeouts.
Starting with Firefox 150, multiple import maps per document are now supported in Nightly builds, giving web developers more flexibility when structuring and loading modern JavaScript modules. This is considered experimental as we gather feedback before enabling it in regular releases.
This feature is part of 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 150, the rendering of absolutely positioned elements across multi-column containers and in printing is improved in Nightly builds, ensuring a more accurate element positioning and fragmentation.
A new CSSContainerRule.conditions property was introduced, holding an array of all container query conditions. This new property is intended to replace CSSContainerRule.containerName and CSSContainerRule.containerQuery, which only supported a single name and query, making them obsolete.
@container rules now allow specifying a list of container query conditions instead of just one condition.
Temporary site permissions are now correctly reflected in the Permissions API.
Firefox improves the rendering of absolutely positioned elements across multi-column containers and in printing, ensuring a more accurate element positioning and fragmentation.
Firefox now supports the declarative definition of slot assignment behaviour for shadow roots.
Container style queries are now supported allowing to apply styles to an element based on the computed values of custom properties of their container. This can be done by using one or more style() functions inside @container rules.
Firefox now supports the Document Picture-in-Picture API, which allows web pages to place content in an always-on-top popup.
The new Fullscreen Keyboard Lock API adds an optional argument to requestFullscreen that allows websites to request that while fullscreen, pressing the Escape key will no longer exit fullscreen (instead, a long-press is required), and certain formerly-reserved browser hotkeys are allowed to be default-prevented.
You can now manage microcontrollers that support serial communications in Firefox via the Web Serial API. This lets you program Microcontrollers and development boards, such as ESP devices, BBCmicro:bit and Raspberry Pi Picos, 3D printers & CNC machines, and other supported devices.
Updated the behavior of implicit anchors in CSS Anchor Positioning. The position-anchor property now defaults to normal. When using position-area, implicit anchors are applied automatically, while popovers using anchor() or anchor-center now require position-anchor: auto to opt in.
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