Firefox 129 for developers

This article provides information about the changes in Firefox 129 that affect developers. Firefox 129 is the current Beta version of Firefox and ships on August 6, 2024.

Changes for web developers

Developer Tools

HTML

Removals

CSS

  • The @starting-style CSS at-rule is supported. This lets you define starting values for properties set on an element that you want to transition from when the element receives its first style update. Currently animating from display: none; is not supported (Firefox bug 1834876 and Firefox bug 1834877).

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 newly shipped in Firefox 129 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.

Older versions