Firefox 159 release notes for developers (Stable)

Changes for web developers

HTML

No notable changes.

CSS

• Scroll-driven animations are now enabled by default. They allow you to animate property values along a scroll-based timeline (that is, by scrolling a scroll container) rather than along the default time-based document timeline. (Firefox bug 1324602).

Removals

• The legacy masonry layout syntax has been removed: the masonry value of the grid-template-columns and grid-template-rows properties, and the masonry-auto-flow property. This syntax was only enabled by default in Nightly, behind the layout.css.grid-template-masonry-value.enabled preference. It's superseded by grid lanes layout, which uses the grid-lanes and inline-grid-lanes values of the display property. (Firefox bug 2077170).

JavaScript

No notable changes.

APIs

• Methods that sanitize HTML with the HTML Sanitizer API, such as Element.setHTML(), now remove unwanted elements and attributes as the markup is parsed, instead of parsing all of the markup first and then cleaning up resulting DOM tree afterwards. The result is the same, except that neighboring text now lands in a single text node instead of being split across several. (Firefox bug 2070498).
• The WebGL EXT_clip_control extension is now available on devices whose graphics driver supports it. Its clipControlEXT() method changes how clip-space coordinates map to window coordinates: it can move the clip origin to the upper-left corner, and set the depth range in normalized device coordinates to 0 to 1 instead of the default -1 to 1, matching the conventions of Direct3D and WebGPU. The 0 to 1 depth range also makes the reversed-Z technique effective, which improves depth precision with a floating-point depth buffer. (Firefox bug 1885031).
• The WebGL EXT_texture_mirror_clamp_to_edge extension is now available on devices whose graphics driver supports it. It adds the MIRROR_CLAMP_TO_EDGE_EXT texture wrapping mode: texture coordinates from -1 to 0 sample a mirror image of the texture, and coordinates below -1 or above 1 clamp to its edge. This allows a symmetric image, such as a glow, to be stored as a texture containing only half of it. (Firefox bug 1908749).
• The WebGL 2 EXT_texture_norm16 extension is now enabled by default on devices whose graphics driver supports 16-bit normalized formats. It adds 16-bit normalized texture and renderbuffer formats, which store data such as elevation maps and medical images with more precision than 8-bit formats. (Firefox bug 1735401).

DOM

• Scoped custom element registries are now supported, this allows a shadow tree to create an independent CustomElementRegistry whose definitions only apply to that specific DOM subtree. This can be used to avoid collisions where multiple web components declare elements with the same name. The customElementRegistry property can be used on Document, Element, and ShadowRoot. The CustomElementRegistry() constructor creates a new CustomElementRegistry object for scoped usage. (Firefox bug 2070506)

WebDriver conformance (WebDriver BiDi, Marionette)

General

• Recommended preferences are now set as default values instead of user values, so they no longer remain in prefs.js after an unclean shutdown. (Firefox bug 2074275).
• Removed the --remote-allow-system-access command line argument. To enable system access, set the MOZ_REMOTE_ALLOW_SYSTEM_ACCESS environment variable to 1 instead. (Firefox bug 2054896).
• Fixed a memory leak where internal polling operations kept running until shutdown after timing out with an error. This could affect a variety of commands (e.g., WebDriver BiDi's browsingContext.traverseHistory). (Firefox bug 2079758).

WebDriver BiDi

• Implemented the emulation.setMediaFeaturesOverride command, which allows clients to override the values of CSS media features. Currently only prefers-color-scheme is supported. (Firefox bug 2064354).
• Added a machine-readable CDDL (Concise Data Definition Language) file for the Firefox-specific extensions to WebDriver BiDi. (Firefox bug 2057588).

Experimental web features

These features are shipping in Firefox 159 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.

• CSS numeric factory functions exposed in workers and worklets: layout.css.namespace.exposed-in-workers-and-worklets

  The numeric factory functions of the CSS namespace, such as CSS.px(), are now exposed in workers and paint worklets, not only on Window. They're part of the CSS Typed Object Model API, so outside Nightly they also need the layout.css.typed-om.enabled preference set to true. (Firefox bug 2079188).

• New MathMLAnchorElement properties: mathml.a.element.enabled

  The MathMLAnchorElement interface now supports the download, ping, rel, relList, and referrerPolicy properties. (Firefox bug 2064612).