Firefox 125 release notes for developers

Changes for web developers

HTML

No notable changes.

CSS

• The align-content property has been updated to work with display: block; layouts. This brings all the layout positions from flex and grid to block, enabling developers to align block-level elements without converting their container to a flex or grid container. (Firefox bug 1882853).
• The CSS property transform-box now supports the values content-box and stroke-box. For the reference box, the content-box value uses the content box and the stroke-box value uses the stroke bounding box that contains an SVG's shape (Firefox bug 1868374).
• The content-visibility CSS property value auto is now enabled by default. This allows content to skip rendering if it is not relevant to the user. (Firefox bug 1874874).

JavaScript

• Intl.Segmenter is now supported, allowing developers to perform locale-sensitive text segmentation of a string. This enables, for example, splitting a string into words in languages that don't use spaces to separate them: Intl.Segmenter("ja-JP", { granularity: "word" }). You can also split strings into graphemes or sentences. (Firefox bug 1423593, Firefox bug 1883914.)

APIs

• The Popover API is now fully supported, allowing the creation of top level "popover" UI elements that might be used for action menus, custom "toast" notifications, form element suggestions, content pickers, and so on. The popover and its triggering button/input can be created using either HTML attributes or JavaScript, and styled using CSS.

  The following Web APIs are implemented:

  • HTMLButtonElement properties popoverTargetElement and popoverTargetAction.
  • HTMLInputElement properties popoverTargetElement and popoverTargetAction.
  • HTMLElement property popover, hidePopover(), showPopover(), and togglePopover() methods, and beforetoggle and toggle_event events (of type ToggleEvent).

  The following CSS pseudo class and element are now supported for use with popovers:

  • :popover-open
  • ::backdrop has been extended to support popovers

  The following HTML global attributes are supported:

  • popovertarget
  • popovertargetaction

  (Firefox bug 1823757, Firefox bug 1866993).

• The RTCIceTransport properties state and gatheringState, and their associated events statechange and gatheringstatechange, are now supported, along with the RTCDtlsTransport.iceTransport property (which returns the underlying RTCIceTransport for a RTCDtlsTransport). These allow much finer-grained monitoring than provided by the RTCPeerConnection properties iceGatheringState and connectionState. (Firefox bug 1811912)

• Element.ariaBrailleLabel and Element.ariaBrailleRoleDescription are now supported, respectively reflecting the global ARIA HTML attributes aria-braillelabel and aria-brailleroledescription. (Firefox bug 1861201).

• Added support to allow web applications to gracefully recover if a canvas temporarily loses its 2D context, which might happen if the canvas is running hardware-accelerated on a GPU, and its driver crashes (Firefox bug 1887729). Here are some additional details on the events for lost and restored canvas contexts:

  • Applications can monitor for contextlost and contextrestored events, which are fired on at HTMLCanvasElement when the context is lost and recovered, respectively, and can also check the context using CanvasRenderingContext2D.isContextLost().
  • After emitting contextlost, a browser will try and restart the lost context, by default, but code can prevent this by cancelling the event.
  • Offscreen canvases can be monitored in the same way, but using OffScreenCanvas events contextlost and contextrestored, along with OffscreenCanvasRenderingContext2D.isContextLost().

• Added support for the shadowrootclonable attribute of the <template> element, and the shadowRootClonable property of the HTMLTemplateElement interface that reflects it. These set the clonable property of a ShadowRoot that has been created declaratively using the <template> element. (Firefox bug 1880188).

• The readText() method of the Clipboard interface is now supported for asynchronously reading text from the system clipboard. When reading clipboard data that is not provided by the same-origin page, a paste context menu will appear for the user to confirm. (Firefox bug 1877400).

Media, WebRTC, and Web Audio

• The AV1 codec is now supported for Encrypted Media Extensions, enabling higher-quality playback from video streaming providers. (Firefox bug 1601817).

Removals

• The SVGAElement.text property has been removed. The textContent property (inherited from Node) is broadly supported and should be used instead. (Firefox bug 1880689).

WebAssembly

• Support has been added for Wasm modules to use multiple independent linear memories. Multiple memories enable more efficient interoperability between modules and better polyfills for upcoming Wasm standards. They can be used, for example, to create separate memory for internal and shared data, ephemeral and persisted data, or data that needs to be shared between threads. The memory can be created in JavaScript and imported into the Wasm module, or created in the Wasm module and exported. Each new linear memory in a Wasm instance is given a sequential index, starting from zero. WebAssembly memory instructions use the index to reference the memory on which they are operating, defaulting to the first memory defined if no index is specified. For more information, see WebAssembly Memory in Understanding WebAssembly text format. (Firefox bug 1860816).

WebDriver conformance (WebDriver BiDi, Marionette)

General

• Added support for the "userAgent" capability which identifies the default User-Agent value of the endpoint node (Firefox bug 1885495).

WebDriver BiDi

• Added support for the input.setFiles command which allows to set or update the files for <input> elements with type="file" (Firefox bug 1855040).
• Added support for the storage.deleteCookies command to delete cookies (Firefox bug 1854581).
• Added support for "userContext" as a field of the "partition" argument for cookie commands (Firefox bug 1875255).
• Fixed an issue where storage.getCookies would not retrieve all expected cookies for a given "sourceOrigin" (Firefox bug 1884647).
• Fixed an issue where recommended preferences would not be applied if only WebDriver BiDi as remote protocol, which means CDP is disabled, was enabled (Firefox bug 1882748).
• Fixed an issue where creating and switching to a new tab would not wait for the visibilityState to be updated (Firefox bug 1877469).

Changes for add-on developers

• The content of the proxy.ProxyInfo property proxyAuthorization is now passed to the Proxy-Authorization request header sent to HTTP proxies (in addition to the existing support for HTTPS proxies) as part of a CONNECT request (Firefox bug 1794464).

Experimental web features

These features are shipping in Firefox 125 but only in developer releases or behind a preference. To try these out, you can search for the related preference on the about:config page to see if they're enabled or disabled. To learn more about these features, see the Experimental features page.

• CSS transition-behavior: layout.css.transition-behavior.enabled.

  The transition-behavior property is enabled by default in the Nightly release. Authors can use this property to control whether to apply CSS transitions to properties with a discrete animation type (Firefox bug 1882408, Firefox bug 1805727).

• UA styles for <h1> nested into sectioning elements: layout.css.h1-in-section-ua-styles.enabled.

  The <h1> heading doesn't decrease in font size now when nested within sectioning elements <article>, <aside>, <nav>, and <section>. The UA styles for <h1> nested within sectioning elements are no longer relevant since the outline algorithm has been removed from the HTML specification. (Firefox bug 1883896).

  Note: The preference for this feature works in reverse: it's set to false in the Nightly build, which removes the UA styling for headings nested in sectioning elements. It's set to true in all other channels, which retains the existing UA styling for the nested headings.