Firefox 140 for developers

This article provides information about the changes in Firefox 140 that affect developers. Firefox 140 is the current Nightly version of Firefox and ships on June 24, 2025.

Changes for web developers

Developer Tools

HTML

Removals

CSS

Removals

JavaScript

Removals

SVG

Removals

HTTP

Removals

Security

Removals

APIs

DOM

Media, WebRTC, and Web Audio

Removals

WebAssembly

Removals

WebDriver conformance (WebDriver BiDi, Marionette)

General

WebDriver BiDi

Marionette

Changes for add-on developers

Removals

Other

Experimental web features

These features are shipping in Firefox 140 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.

  • Notification.maxActions (Nightly): dom.webnotifications.actions.enabled

    The Notification.maxActions read-only static property returns the browser limit on the number of actions that can be associated with a Notification, which you create using ServiceWorkerRegistration.showNotification(). This was released prematurely in Firefox version 138, and this change makes it available only in the Nightly build. (Firefox bug 1963263).

  • Prioritized Task Scheduling API (Nightly release). The Prioritized Task Scheduling API provides a standardized way to prioritize all tasks belonging to an application, whether they are defined in a website developer's code, or in third-party libraries and frameworks. This adds support for the TaskSignal.any() static method, which returns a signal that is triggered when any of the TaskSignal objects it is created from are triggered. The API is now feature complete. (Firefox bug 1964407).

Older versions