Firefox 155.0

New

• Smart Window is now available for all users in the USA, Canada, and France to try out! Additionally, Firefox 155 includes many new enhancements:
• New personalized resume conversation starters help users quickly return to topics they’ve been working on.
• Assistant now responds much faster with Exa web search source citations to provide accurate, trustworthy web grounding in roughly 1/5 the time.
• Organize Tabs now suggests better groupings of your related tabs and gives each group a clearer, more descriptive name. This feature is part of a progressive roll out. What is 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.
• Firefox now shows how many trackers it has blocked in the address bar, making built-in privacy protections easier to see while browsing. The count can be hidden in settings without turning off tracker blocking. This feature is part of a progressive roll out. What is 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.
• Nintendo Switch Pro and compatible aftermarket controllers now work fully in web games on Windows, with the directional pad and analog sticks correctly mapped.
• Containers can now be reordered in Settings, and the new order is used wherever containers are listed.
• The Translations feature now supports the following languages:
• Marathi
• Urdu

Fixed

• Fixed text disappearing in Microsoft 365 Word Online and other web apps on Linux when typing with certain keyboard layouts.
• Fixed an unnecessary paste confirmation appearing when using the keyboard shortcut to paste without formatting in Google Docs.
• Firefox now recovers from the toolbar and tab strip being left unresponsive when the platform fails to end a tab drag session.
• 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.
• Fixed the sound indicator disappearing from a tab that was moved to another window, leaving no way to see or mute what was playing.
• Fixed Firefox preventing Linux systems from going to sleep after a long browsing session.
• Fixed full screen content being letterboxed on MacBooks with a camera notch, most visibly when watching video.
• 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 web pages on Windows.
• Fixed WebCodecs VideoEncoder hanging on macOS when encoding a VideoFrame in NV12 format.
• Various security fixes.

Changed

• 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.
• 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.
• 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%.

Enterprise

• You can find information about policy updates and enterprise-specific bug fixes in the Firefox for Enterprise 155 Release Notes.

Developer

• Developer Information
• 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 at-rules (@) button.
• 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.
• 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.

Web Platform

• 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.
• Firefox now supports the progress() CSS function.
• 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.
• Firefox now supports the Promise.allKeyed and Promise.allSettledKeyed methods from the await dictionary proposal, which take an object of promises and resolve to an object of results with the same keys.
• 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.
• 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).
• 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.
• SVG elements now expose the same URL properties as HTML links, including protocol, host, pathname, and search.
• SVGGraphicsElement.getBBox() now honors its options argument, so bounding boxes can include stroke, markers, and clipping.
• 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 now supports send groups (createSendGroup()) for controlling how bandwidth is shared between streams, writable datagram streams (createWritable()), and exportKeyingMaterial() for deriving keys bound to the TLS session. It also adds a draining promise and subprotocol negotiation through the constructor's protocols option and the protocol property.
• Firefox now supports RTCError for data channel failures, RTCSctpTransport.maxChannels, two-byte RTP header extension IDs, and more accurate RTCTransportStats, improving WebRTC interoperability.

Unresolved

• For users with vertical tabs enabled, the sidebar may not persist across Firefox restarts. Vertical tabs can be re-enabled after the restart by clicking the sidebar toolbar button. A fix is currently in development. (Bug 2065431)
• Some sites may load slowly or fail to load on networks that block UDP. This can affect e.g. corporate networks where a proxy or firewall blocks QUIC as part of TLS inspection. To work around it, set network.http.happy_eyeballs_enabled to false with the Preferences policy. A fix is planned for the 155.0.1 release shipping no later than 8-September. (Bug 2063452)

Community Contributions

• With the release of Firefox 155, we are pleased to welcome the developers who contributed their first code change to Firefox in this release, 20 of whom were brand new volunteers! Please join us in thanking each of these diligent and enthusiastic individuals, and take a look at their contributions:
• Artem Bilous: 2056733
• Cameron: 2052559, 2052619
• Colden Cullen: 2060708
• Dan: 1735300
• Fede: 1418178, 2040498, 2046774
• Giulio B: 2048884
• K: 1642578
• Kevin Gosse: 2054036
• Michael F: 2052438
• mikey gough: 2053551
• munawiki: 2055309
• Nathan Leuz: 2053550
• Nirmal Advani: 1804108, 2003174, 2003177, 2003181, 2031618, 2033570, 2046156, 2052618, 2053543, 2053566, 2053568, 2053977, 2058556, 2059866, 2060649
• Priyanshu[:0xanshu]: 1977947
• Richard Van Natta[:rnvannatta]: 2052617
• Ruhollah Majdoddin: 1856645, 2060029, 2061166, 2061348
• Shawn Zivontsis: 2025999
• Simon Rosen: 1875517
• Yuxiao Zhu: 1861034
• Zyphrenn: 2033961, 2059969