Firefox 160 release notes for developers (Beta)

Changes for web developers

APIs

• The WebTransport() constructor now accepts the headers option, which adds custom HTTP headers to the extended CONNECT request that sets up the session. The headers that the server sends in its response are available in the WebTransport.responseHeaders property once the session is established. (Firefox bug 2081470, Firefox bug 2033220).
• The WebTransport.exportKeyingMaterial() method has been updated to match the current specification. The context argument is now required, and a new outputLength argument specifies the number of bytes of keying material to derive. Previously, the method always returned 32 bytes. Code that omits either argument will need to be updated. (Firefox bug 2079306).
• The incomingMaxBufferedDatagrams and outgoingMaxBufferedDatagrams properties of the WebTransportDatagramDuplexStream interface are now supported. They replace the non-standard incomingHighWaterMark and outgoingHighWaterMark properties, which have been removed. These properties represent the maximum number of incoming datagrams that can be queued while waiting to be read, and the maximum number of outgoing datagrams that can be queued for sending before backpressure is applied. (Firefox bug 2023587).
• The WebTransport() constructor now supports the datagramsReadableType option. Setting it to bytes makes the transport's stream of incoming datagrams, transport.datagrams.readable, a readable byte stream. You can then use a ReadableStreamBYOBReader to read each datagram into a buffer that you supply and reuse, instead of receiving a new Uint8Array for every datagram. (Firefox bug 2007755).

Changes for add-on developers

• runtime.PlatformInfo now returns arch as arm64 for ARM64 platforms. Previously, it returned aarch64. This aligns the value returned by Firefox for ARM64 platforms with Chrome. (Firefox bug 2080310)

Experimental web features

These features are shipping in Firefox 160 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.

• CSSNumericValue arithmetic methods: layout.css.typed-om.enabled

  The add(), sub(), mul(), and div() methods of the CSSNumericValue interface in the CSS Typed Object Model API are now supported in Nightly. They add, subtract, multiply, or divide numeric values, respectively; for example, CSS.px(10).add(CSS.px(5)) adds two pixel values. The result is a CSSUnitValue (15px in this example) when it can be simplified to a single unit, or a math expression such as a CSSMathSum when it can't be simplified (for example, when adding px to %). (Firefox bug 2081689).