Firefox 158 release notes for developers (Stable)

Changes for web developers

Accessibility

• The aria-busy attribute is now supported in Firefox for Android (desktop support has been available for a long time). This ARIA state indicates whether an element is currently being modified. It allows assistive technologies to wait until changes to the content are complete before informing users of the update. For example, a screen reader can wait until a live region has finished updating before announcing the changes. (Firefox bug 908042).

HTML

No notable changes.

CSS

• CSS typed arithmetic is now supported, which enables using functions such as calc() to divide two values of the same data type, even if they use different units. The resulting unitless quotients can then be converted to other data types, creating useful relationships between different values on a page. (Firefox bug 2067411).

JavaScript

No notable changes.

HTTP

• The default HTTP Accept header for image requests now includes image/jxl, following support for the JPEG XL image format. The new value is image/avif,image/jxl,image/webp,image/png,image/svg+xml,image/*;q=0.8,*/*;q=0.5 (see List of default Accept values). (Firefox bug 2065096).

APIs

• The WebTransport.getStats() method is now supported. This method returns statistics for the transport's underlying connection and its datagrams. (Firefox bug 2007202).
• The WebTransport.supportsReliableOnly static property is now supported. This property indicates whether the browser supports WebTransport sessions over exclusively reliable transports, such as HTTP/2. Firefox doesn't support WebTransport over HTTP/2 yet, so the property always returns false. (Firefox bug 2007783).
• The navigate option of the Notification() constructor and the ServiceWorkerRegistration.showNotification() method is now supported. This option specifies a URL to navigate to after the user clicks the generated system notification. Once a notification is created, you can retrieve the URL from the Notification.navigate property. (Firefox bug 2069920).
• The WebGPU float32-blendable feature is now supported (see GPUSupportedFeatures). This allows blending of GPUTextures that use the r32float, rg32float, or rgba32float format. (Firefox bug 1931630).
• The WebGPU clip-distances feature is now supported on macOS (see GPUSupportedFeatures). This allows vertex shaders to output clip_distances in WGSL, which cut away the parts of a triangle or line that fall on one side of a custom plane, while the rest is still drawn. This is useful for effects such as reflections in water or cutaway views in CAD applications. (Firefox bug 1931629).
• The WebGL EXT_polygon_offset_clamp extension is now available on compatible devices. Its polygonOffsetClampEXT() method works like polygonOffset(), with an extra argument that limits the depth offset. This helps avoid holes in shadows when using shadow mapping. (Firefox bug 1854003).
• The PerformanceResourceTiming.deliveryType property is now supported, which indicates how a resource was delivered. The initial release supports the cache value, which indicates that the resource came from the cache. (Firefox bug 1914120, Firefox bug 2071913).

DOM

• The SVGGraphicsElement.getBBox() method now honors the fill and stroke properties of its options argument when called on <tspan> and <textPath> elements. This allows you to get a bounding box that includes the stroke of a text span, as you already could for a whole <text> element. (Firefox bug 2072680).
• The javascriptURLs option of the HTML Sanitizer API configuration and the Sanitizer.setJavascriptURLs() method are now supported. They set whether a sanitizer removes attributes that contain javascript: URLs, such as <a href="javascript:…">, when it's used with an unsafe method like Element.setHTMLUnsafe(). The safe methods, like Element.setHTML(), still always remove them. As a result, the unsafe methods now remove javascript: URLs when used with the default sanitizer, or with a sanitizer after Sanitizer.removeUnsafe() is called. (Firefox bug 2068934).

Media, WebRTC, and Web Audio

• When sending H.264 or AV1 video with WebRTC, Firefox now lowers the resolution and frame rate as needed to stay within the codec level negotiated with the remote peer, set by the profile-level-id parameter for H.264 and level-idx for AV1. As a result, MediaCapabilities.encodingInfo() now reports a webrtc configuration as supported even if its resolution and frame rate exceed the level in its contentType. (Firefox bug 2013936).

WebDriver conformance (WebDriver BiDi, Marionette)

General

• Added support for setting the camera and microphone permissions with the permissions.setPermission command in WebDriver BiDi and the WebDriver:SetPermission command in Marionette. This allows tests to grant or deny access to media devices without prompting the user. (Firefox bug 2070577).
• Changed the touch start and touch move tolerances to zero in automation, so that touch actions now scroll from exactly the position at which they are dispatched, without small initial movements being absorbed. (Firefox bug 2055661).

WebDriver BiDi

• Added support for the imageSize argument to the browsingContext.captureScreenshot command, which allows clients to specify the maximum size of the resulting screenshot image. (Firefox bug 2069002).
• Added support for the destinationFolder argument to the browsingContext.startScreencast command, which allows clients to choose the folder where the recorded video file is saved. (Firefox bug 2072616).

Marionette

• Fixed the WebDriver:TakeScreenshot command to return an unable to capture screen error when the width or height of the captured image is zero. (Firefox bug 1492357).

Other

• Support for the JPEG XL image format (image/jxl) is now enabled by default. JPEG XL is a royalty-free raster image format that supports lossy and lossless compression, transparency, animation, and HDR. It can also losslessly transcode existing JPEG images. (Firefox bug 2065096).

Changes for add-on developers

• publicSuffix.isKnownSuffix() now throws an error when passed an invalid hostname, instead of returning false. (Firefox bug 2066620)
• Adds runtime.getVersion() to return the extension's version as declared in the manifest. (Firefox bug 1992418)

Experimental web features

These features are shipping in Firefox 158 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.

• random() CSS function: layout.css.random.enabled

  The random() CSS function generates a random value within a specified range, optionally limiting the possible values to step size intervals between those limits. An optional <random-key> parameter controls which random() functions share a random value, for example across elements or properties. (Firefox bug 2071165).

• corner-shape properties: layout.css.corner-shape.enabled

  The corner-shape shorthand property and its constituent longhand properties are now supported in Nightly. These properties let you customize corner shapes using one of the <corner-shape-value> keyword values or the superellipse() function. (Firefox bug 2070927).

• Deferred module evaluation (Nightly): javascript.options.experimental.defer_import_eval

  The import defer declaration and the import.defer() syntax are now available in Nightly behind a preference. They load a module and its dependencies up front, but run the module's code only when one of its exports is first accessed, so modules that aren't needed right away don't slow down startup. Modules that use top-level await still run right away. (Firefox bug 1952263).

• On-device speech recognition: media.webspeech.recognition.enable

  On-device speech recognition is now supported in Nightly, on desktop only. This allows you to perform speech recognition via the Web Speech API directly in the browser, rather than relying on a cloud service. (Firefox bug 2069803).

• Speculation rules: moderate eagerness: dom.speculation_rules.enabled

  The Speculation Rules API provides a mechanism to improve performance for future navigations by specifying which resources should be prefetched or prerendered based on factors such as user behavior towards links. Firefox 158 Nightly adds support for moderate eagerness: a matching prefetch starts once the user hovers over a link for a short time (200 milliseconds by default). (Firefox bug 2061013).

• Streaming request bodies: dom.fetch.streaming_upload

  Enabled in Nightly only, you can now set a ReadableStream as a request body (for example, via the Request() constructor or the Window.fetch() method). This allows you to stream uploads incrementally rather than having to wait for the whole body to be available. (Firefox bug 1594633).

• CSSNumericValue.equals(): layout.css.typed-om.enabled

  The CSSNumericValue.equals() method of the CSS Typed Object Model API is now supported in Nightly. It returns true if every value passed to it is the same as the numeric value it's called on, and false otherwise. Values are compared as written, without converting units. For example, 1in and 2.54cm are different, as are calc(1px + 2px) and calc(2px + 1px). (Firefox bug 2074503).