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Firefox 143 release notes for developers

files/en-us/mozilla/firefox/releases/143/index.md

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This article provides information about the changes in Firefox 143 that affect developers. Firefox 143 was released on September 16, 2025.

Changes for web developers

HTML

  • The type="color" {{HTMLElement("input")}} element now accepts not only HEX colors like #ff6699 but also all CSS <color> values, for example oklab(50% 0.1 0.1 / 0.5). (Firefox bug 1965029).

CSS

  • The {{cssxref("::details-content")}} pseudo-element is now enabled by default. It lets you style the content of the {{htmlElement("details")}} element. (Firefox bug 1941406).
  • The {{cssxref("::marker")}} pseudo-element can now be used to style a list item that has been created using the {{cssxref("::before")}} or the {{cssxref("::after")}} pseudo-element. This is achieved using the ::before::marker and ::after::marker selectors. (Firefox bug 1980215).
  • Multi-pass grid track sizing is now enabled by default and follows the algorithm outlined in the CSS Grid specification. In the multi-pass algorithm, columns are sized first, then rows; percentage values are resolved after the container size is known. With this default support, percentage-based row tracks and grid items with aspect ratios will now be sized correctly in more cases. (Firefox bug 1957244).

JavaScript

No notable changes.

APIs

Removals

  • The deprecated {{domxref("CompositionEvent.locale")}} property is no longer supported. (Firefox bug 1700969).

WebDriver conformance (WebDriver BiDi, Marionette)

WebDriver BiDi

  • Updated the browsingContext.contextCreated event to be emitted for all open contexts when subscribing to the event (Firefox bug 1754273).
  • Implemented new commands for the network module to enable recording network data:
    • network.addDataCollector adds a network data collector to contexts, userContexts or globally. The collector will record network data corresponding to the provided dataTypes. At the moment, only the "response" data type is supported. A maxEncodedDataSize must also be provided, network data exceeding this size will not be recorded (Firefox bug 1971778).
    • network.removeDataCollector removes a previously added network data collector (Firefox bug 1971781).
    • network.getData retrieves the data collected for a provided request id, dataType and optionally collector id. When providing a collector id, clients may also pass the disown flag to release the network data from the collector. Note that data is deleted when it is no longer owned by any collector (Firefox bug 1971780).
    • network.disownData releases the data for a given request id and dataType from the provided collector id (Firefox bug 1971779).
  • Fixed a bug where emulation.setLocaleOverride did not apply the override to newly created cross-origin iframes (Firefox bug 1978533).
  • Fixed a bug where several commands such as session.subscribe would fail if any tab was unloaded (Firefox bug 1949037).
  • Fixed the browsingContext.navigationCommitted event so that the url property now includes basic auth credentials. (Firefox bug 1980137).

Changes for add-on developers

  • Addition of {{WebExtAPIRef("storage.StorageArea.getKeys()")}}. This method returns an array containing all of the keys in a storage area. It's available for all storage areas, that is {{WebExtAPIRef("storage.sync", "sync")}}, {{WebExtAPIRef("storage.local", "local")}}, {{WebExtAPIRef("storage.session", "session")}}, and {{WebExtAPIRef("storage.managed", "managed")}}. (Firefox bug 1910669)
  • User selection of an extension suggestion in the address bar (omnibox), an action that fires {{WebExtAPIRef("omnibox.onInputEntered")}}, is now considered a user action. In addition to enabling the APIs that require a user action, selecting an extension suggestion in the address bar also grants the "activeTab" permission.

Experimental web features

  • text-autospace: layout.css.text-autospace.enabled

    The text-autospace CSS property allows you to specify the space applied between Chinese/Japanese/Korean (CJK) and non-CJK characters. Currently these values are only parsed and there is no effect on the output. (Firefox bug 1869577).

  • WebGPU external textures: dom.webgpu.external-texture.enable

    The GPUExternalTexture interface and GPUDevice.importExternalTexture() method are supported for importing external textures from video frames or elements. (Firefox bug 1979100).

These features are shipping in Firefox 143 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.