Firefox 154 release notes for developers (Beta)

Changes for web developers

APIs

Media, WebRTC, and Web Audio

• The RTCIceTransport.getSelectedCandidatePair() method and selectedcandidatepairchange event are now supported for getting the current RTCIceCandidatePair for the transport. (Firefox bug 2019332).
• The error event is now fired on RTCDtlsTransport to report DTLS and fingerprinting errors. (Firefox bug 1805447).

WebDriver conformance (WebDriver BiDi, Marionette)

General

• Improved the handling of deltaX and deltaY properties for asynchronous widget wheel scroll events by taking the layout viewport into account. (Firefox bug 1971979).
• Fixed a bug where a navigation would resolve prematurely for subframes when calling history.replaceState or when navigating to an error page (e.g., blocked by X-Frame-Options). (Firefox bug 2051908).

WebDriver BiDi

• Added a download id to browsingContext.downloadWillBegin and browsingContext.downloadEnd events to make it easier to identify which events belong to the same download. (Firefox bug 2040936).
• Added support for an ignore state for the unhandledPromptBehavior property for file pickers when creating a new session with the session.new command. With this state, file pickers will not be handled automatically by the protocol. (Firefox bug 1999693).
• Added a userContext field (a.k.a. Firefox container) to the payload of several WebDriver BiDi events and commands, which makes it easier to filter out incoming data for clients subscribing to events by user context id. (Firefox bug 2018611).
• Implemented the browsingContext.startScreencast and browsingContext.stopScreencast commands, which will record a browsing context and save the result as a video file. (Firefox bug 2042671).
• Updated the emulation.setLocaleOverride command to allow overriding the Accept-Language header for fetch and WebSocket requests in workers. (Firefox bug 2052932).
• Fixed a bug where the script.realmDestroyed event was missing for a worker after cross-process navigation. (Firefox bug 2018154).

Changes for add-on developers

• Adds support for the sandbox manifest key, enabling extensions to designate pages that load with an opaque origin, without direct access to extension APIs. A sandboxed page can use eval() and similar constructs that are otherwise blocked by the extension's content security policy. (Firefox bug 1685123)

Experimental web features

These features are shipping in Firefox 154 but are disabled by default. To experiment with them, search for the appropriate preference on the about:config page and set it to true. You can find more such features on the Experimental features page.

• Truncating content with line-clamp: layout.css.line-clamp.enabled

  The line-clamp CSS property now works without the -webkit- vendor prefix, though at this stage it does not support the no-ellipsis and <string> values. (Firefox bug 2042986).

• Percentage values for text-decoration-inset: layout.css.text-decoration-inset-percentage.enabled

  The text-decoration-inset CSS property now supports percentages as values. The percentage value specifies the size of the inset as a percentage of the font-size. (Firefox bug 2044602).

• CSS Typed Object Model Level 1 (Nightly): layout.css.typed-om.enabled

  The CSS Typed Object Model API (as defined in the CSS Typed Object Model Level 1 specification) is now implemented. This simplifies CSS property manipulation by exposing CSS values as typed JavaScript objects rather than strings. (Firefox bug 2051047).