Firefox 144 for developers

This article provides information about the changes in Firefox 144 that affect developers. Firefox 144 is the current Beta version of Firefox and ships on October 14, 2025.

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

Changes for web developers

MathML

Removals

  • Support for the deprecated MathML STIXGeneral font has now been removed. The setting mathml.stixgeneral_operator_stretching.disabled has also been removed. (Firefox bug 1336058).

CSS

APIs

DOM

Media, WebRTC, and Web Audio

WebDriver conformance (WebDriver BiDi, Marionette)

WebDriver BiDi

  • Implemented the new browsingContext.downloadWillBegin event, which is emitted when a new download is initiated, either by clicking a link with the download attribute, or in response to a network request with a Content-Disposition header indicating a file attachment (Firefox bug 1874365).

  • Implemented the new emulation.setScreenOrientationOverride command, which allows clients to emulate different screen orientations. This command is not limited to mobile devices, but also works for desktop applications (Firefox bug 1974167).

  • Implemented the new emulation.setTimezoneOverride command, which allows clients to simulate a specific timezone setting (Firefox bug 1978027).

  • Enhanced the emulation.setLocaleOverride command to also apply the specified settings to sandboxes previously created via WebDriver BiDi (Firefox bug 1983807).

  • Fixed a bug where the locale override set via emulation.setLocaleOverride was sometimes incorrectly shared between different browsing contexts within the same process (Firefox bug 1980211).

  • Enhanced the browsingContext.navigate command to avoid NS_BINDING_ABORTED errors caused by redirects or interruptions occurring after the navigation was already committed (Firefox bug 1914407).

Marionette

  • Reverted the Scroll Into View WebDriver algorithm as used by several WebDriver classic commands in Marionette to always use the instant scroll behavior. This undoes the change introduced in Firefox 97, which had switched the behavior to auto. The reversion addresses potential race conditions when scrolling elements that use smooth behavior (Firefox bug 1986238).

Changes for add-on developers

Experimental web features

These features are shipping in Firefox 144 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.