Firefox 147 release notes for developers (Beta)

Changes for web developers

CSS

• CSS anchor positioning is now enabled by default. (Firefox bug 1988225).
  • The anchor-center value, which provides a convenient way to center an anchor-positioned element on its anchor, was added in version 147. It is available on the align-items, align-self, justify-items, justify-self, place-items, and place-self properties. (Firefox bug 1909339)
  • The position-anchor value none was added in version 147, which enables an implicit or explicit association between a CSS anchor and an anchor-positioned element to be removed. (Firefox bug 1999972).
• The -webkit- prefixed version of the perspective property is now supported with unitless values — for example -webkit-perspective: 800 — for increased compatibility. (Firefox bug 1362499).
• View transition types are now supported, which provide a mechanism by which different types can be specified for active view transitions. CSS can then be used to apply animations to DOM elements when their content updates, depending on the transition type specified. Firefox 147 adds support for single-page app (SPA) view transition types only, not cross-document view transition types. (Firefox bug 2001878).
• The counter-increment, counter-reset, counter-set, and quotes properties are now supported on the ::marker pseudo-element. (Firefox bug 2000404).

JavaScript

• CSS module scripts are now supported, allowing a stylesheet to be loaded into a script as a CSSStyleSheet instance using the import keyword and the type import attribute set to type="css". (Firefox bug 1986681).

APIs

• The Document.activeViewTransition property is now supported, which returns a ViewTransition instance representing the view transition currently active on the document. This provides a consistent way to access an active view transition in any context without having to manually store a reference to it for later use. (Firefox bug 2001836).
• WebGPU API support is now enabled for all macOS versions on devices with Apple Silicon processors (previously only macOS Tahoe support was enabled). (Firefox bug 1993341).
• The Navigation API is now supported. This provides the ability to initiate, intercept, and manage browser navigation actions, and to examine an application's history entries. This is a successor to previous web platform features such as the History API and window.location, which solves their shortcomings and is specifically aimed at the needs of single-page applications (SPAs). (Firefox bug 1997962).
• Brotli compression is now supported for both CompressionStream and DecompressionStream. (Firefox bug 1921583).
• Service workers can now be ECMAScript module scripts. To load a service worker module, specify a type of 'module' when calling ServiceWorkerContainer.register(). (Firefox bug 1360870).

Changes for add-on developers

Experimental web features

These features are shipping in Firefox 147 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.