Firefox 126 for developers

This article provides information about the changes in Firefox 126 that affect developers. Firefox 126 was released on May 14, 2024.

Changes for web developers

Developer Tools

HTML

No notable changes.

MathML

Removals

  • The automatic adjustment for vertically centered operators (+, =, <, etc.) has been disabled by default. This behavior is not defined in MathML Core and was only necessary as a workaround for non-math fonts. It can still be enabled by setting the mathml.centered_operators.disabled config to false. (Firefox bug 1890531).

CSS

  • The zoom property is now supported. It can be used to increase or decrease the size of an element and its contents (Firefox bug 390936).

JavaScript

No notable changes.

HTTP

APIs

DOM

  • The ability to define states for custom elements and match them using CSS selectors is now available by default. The custom states are represented as custom identifiers that can be added to or removed from the element's ElementInternals.states property (a CustomStateSet). The CSS :state() pseudo-class takes a custom identifier as an argument and matches custom elements if the identifier is present in their set of states (Firefox bug 1887543).
  • The Selection.direction property is now supported for indicating the direction of a range (Firefox bug 1867058).

Media, WebRTC, and Web Audio

Removals

WebDriver conformance (WebDriver BiDi, Marionette)

WebDriver BiDi

  • Added the contexts argument to the network.addIntercept command to limit the interception of network requests to particular top-level browsing contexts (Firefox bug 1882260).
  • Both the commands session.subscribe and session.unsubscribe now raise an invalid argument error when the value of the arguments events or contexts are empty arrays (Firefox bug 1887871).
  • Updated the implementation of the storage.getCookies command to align with the Gecko default cookie behaviour. This allows the removal of the user value for the preference network.cookie.cookieBehavior, which was only expected to be set for our CDP implementation (Firefox bug 1879503).
  • Removed the ownership and sandbox arguments for the browsingContext.locateNodes command because they are no longer necessary (Firefox bug 1884935).
  • Improved error message for the session.new command when no capabilities are specified (Firefox bug 1838152).

Changes for add-on developers

Experimental web features

These features are newly shipped in Firefox 126 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