Firefox 129 for developers

Removals

• 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).
• The transition-behavior CSS property is supported. This lets you specify if descrete properties, such as display and overlay, can be transitioned by setting the value to allow-descrete. (Firefox bug 1901645).
• -webkit-font-feature-settings has been implemented as an alias of the standard font-feature-settings property (Firefox bug 1595620).

Removals

• Float16Array typed arrays are now supported, along with DataView.prototype.getFloat16() and DataView.prototype.setFloat16() for reading and setting Float16Array values from a DataView, and the Math.f16round() static method, which can be used to round numbers to 16 bits. The new type is useful for sharing data with a GPU, in particular for use cases where it makes sense to trade off precision for memory consumption. (Firefox bug 1903329.)
• Regular expressions can now use the same name for named capturing groups in different disjunction alternatives. This is allowed because only one alternative in a disjunction will match, so a name declared in several alternatives can only reference one captured group. The names must still be unique within a particular alternative, and across the rest of the pattern. (Firefox bug 1903288.)

Removals

Removals

Removals

Removals

• The deprecated textInput event is now supported, enabling web apps that use legacy libraries or frameworks that rely on these events. The beforeinput event supersedes textInput, and should always be used by new applications. (Firefox bug 1901923.)
• The default .toJSON() methods GeolocationCoordinates.toJSON() and GeolocationPosition.toJSON() are now supported, enabling serialization of GeolocationCoordinates and GeolocationPosition objects with JSON.stringify() (Firefox bug 1890706).
• CSSPageDescriptors is now supported, and is used as the type for CSSPageRule.style instead of CSSStyleDeclaration — matching the current specification. This ensures that CSSPageDescriptors only exposes the @page related properties, rather than all properties, and also resolves an issue where setting the page size in a CSS @page at-rule was not reflected in CSSPageRule.style. (Firefox bug 1890842, Firefox bug 1867106.)
• MediaCapabilities.decodingInfo() can now get decoding information for a particular encrypted media configuration as well unencrypted media, allowing applications to tell ahead of time if the configuration is supported, and whether it will play the content smoothly and be power efficient. Changes include a new property keySystemConfiguration on the method's configuration argument that defines the properties of the key system used to encrypt the media, and a new keySystemAccess property on the returned object, which is a MediaKeySystemAccess object that can be used to create keys and decode the content for playback. (Firefox bug 1898344).
• Firefox now fires events for a synchronous XMLHttpRequest before firing the events for any ongoing asynchronous XMLHttpRequest. This fixes a long-standing behavioral difference with other browsers. Note that while this should fix some sites, it may also cause degraded performance on sites that expect the old "non-blocking" behaviour for a synchronous XMLHttpRequest. Please file a bug if your website should have been fixed by this change but still appears to have related issues. (Firefox bug 697151.)

DOM

Media, WebRTC, and Web Audio

Removals

Removals

• The Navigator.vibrate() method has been removed (Firefox bug 1653318, Firefox bug 1900037).

General

WebDriver BiDi

Marionette

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.