Firefox Nightly
Release Notes

Starting with Firefox 154, Firefox Nightly is testing a simpler tab context menu in Firefox Labs. It can be turned on in Settings > Firefox Labs > Streamline tab menu, and feedback is welcome on Mozilla Connect.

Fixed Firefox preventing Linux systems from going to sleep after a long browsing session.

Fixed arrow-key and Page Up/Down scrolling not working on some pages with embedded content from other sites.

Fixed characters from some less common scripts appearing as empty boxes on Windows.

Fixed text disappearing in Microsoft 365 Word Online and other web apps on Linux when typing with certain keyboard layouts.

On Firefox for Android, autofill prompts now dismiss when focus moves away instead of remaining open until back navigation.

On Firefox for Android, tabs opened by extensions during private browsing now load in private browsing. Previously they appeared private while their content loaded in regular browsing, which could leave site data behind.

Fixed an unnecessary paste confirmation appearing when using the keyboard shortcut to paste without formatting in Google Docs.

Fixed text inside buttons not being selectable or copyable, which prevented copying direct messages on X and comments on YouTube.

Fixed live audio streams such as internet radio stopping when playing in the background.

Firefox now recovers from the toolbar and tab strip being left unresponsive when the platform fails to end a tab drag session.

Fixed full screen content being letterboxed on MacBooks with a camera notch, most visibly when watching video.

Firefox now opens mailto: links only in response to an explicit user action, so pages can no longer launch the default mail client unprompted.

PDFs smaller than the paper size can now be enlarged to fill the sheet when printing, by setting the scale above 100%.

Firefox now uses firefox-portal-detection.com instead of detectportal.firefox.com to detect captive portals and check network connectivity, so network allowlists referencing the old domain need updating.

On Firefox for Android, long-pressing a toolbar shortcut now offers an Edit shortcut option that goes straight to its setting.

Firefox now limits CSS to 75 levels of nested blocks and functions, preventing crashes that extremely deep nesting can cause under some circumstances. More deeply nested rules and values no longer parse.

The Rules View now offers toggles to emulate the prefers-reduced-motion media feature. Emulation options have also moved into a new panel behind the @ button.

The JSON Viewer now displays JSON Lines (JSONL/NDJSON) documents, including inline errors for invalid lines.

Fixed the Storage panel showing cookies from private windows, containers, and other partitions alongside the inspected page's own cookies.

Uncaught non-Error exceptions now list their property names in the Console instead of showing only Object.

The Debugger in Developer Tools now has a keyboard shortcut, Ctrl+Alt+B (Cmd+Alt+B on macOS), to enable or disable all breakpoints at once.

Starting with Firefox 153, Firefox Nightly ships an experimental implementation of the link-parameters property by Tyler Thrailkill.

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.

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.

Firefox 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.

SVG <a> elements now expose the same URL properties as HTML links, including protocol, host, pathname, and search.

Starting with Firefox 155, the RegExp Buffer Boundary proposal is now available for testing in Nightly builds by setting the javascript.options.experimental.regexp_buffer_boundaries preference.

Starting in Firefox 155, the CSS Typed Object Model's StylePropertyMap now supports delete() for removing a property in Nightly builds.

Starting with Firefox 155, Firefox Nightly offers limited support for the Speculation Rules API for same-origin prefetch, allowing pages to declare which links should be prefetched. This initial support covers only the immediate eagerness level and list source rules.

The CSS attr() function now supports values of any type, so authors can use attribute values in any property rather than only as strings in the content property.

Starting with Firefox 155, Nightly builds enable the Audio Session API, letting sites declare how their audio mixes with other applications.

Starting with Firefox 155, Nightly builds now support the at-rule() function for @supports. This allows authors to test for browser support of specific at-rules, such as @supports at-rule(@scope).

Firefox 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.

SVGGraphicsElement.getBBox() now honors its options argument, so bounding boxes can include stroke, markers, and clipping.

Starting with Firefox 155, Firefox Nightly supports typed arithmetic in CSS calc(), allowing units to be multiplied and divided within math functions.

Firefox now supports the Promise.allKeyed and Promise.allSettledKeyed methods, which take an object of promises and resolve to an object of results with the same keys.

Starting with Firefox 155, Firefox Nightly supports the <a> element in the MathML namespace, exposed via the new MathMLAnchorElement WebIDL interface, so mathematical expressions can be links.

Firefox now supports QUIC version 2 (RFC 9369) for HTTP/3 connections, and uses it when the server selects it through compatible version negotiation (RFC 9368).

Firefox now supports the WebAssembly Compact Import Section proposal, which can reduce the size of WebAssembly modules with many imports.

Firefox now supports the WebAssembly Wide Arithmetic proposal, which adds 128-bit arithmetic instructions for better performance in cryptography and arbitrary-precision math.

Support for the non-standard ::-webkit-scrollbar pseudo-element, added in Firefox 153, is now limited to a small list of sites rather than applying universally.

The font-width property is now supported as the standard name for font-stretch.

A dynamic import() that fails due to a network or HTTP error is no longer cached as a failure in the module map, so retrying the same specifier can now succeed.

WebTransport adds send groups (createSendGroup()) for controlling how bandwidth is shared between streams, exportKeyingMaterial() for deriving keys bound to the TLS session, writable datagram streams (createWritable()), a draining promise, and subprotocol negotiation via the constructor's protocols option and the protocol property.

Firefox 155 improves WebRTC interoperability, adding RTCError for data channel failures, RTCSctpTransport.maxChannels, two-byte RTP header extension IDs, and more accurate RTCTransportStats.