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title Firefox 143 for developers
short-title Firefox 143 (Beta)
slug Mozilla/Firefox/Releases/143
page-type firefox-release-notes-active
sidebar firefox

This article provides information about the changes in Firefox 143 that affect developers. Firefox 143 is the current Beta version of Firefox and ships on September 16, 2025.

Note

The release notes for this Firefox version are still a work in progress.

Changes for web developers

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).

APIs

Removals

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

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).

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.