Firefox 100 for developers

Changes for web developers

HTML

No notable changes.

CSS

• CSS media features for dynamic-range and video-dynamic-range are now supported. You can now test whether a user agent or an output device supports the combination of brightness, contrast ratio, and color depth by using dynamic-range and in the video plane by using video-dynamic-range (Firefox bug 1751217).

JavaScript

No notable changes.

HTTP

Removals

• The non-standard Large-Allocation HTTP header has been removed (Firefox bug 1598759).

APIs

• WritableStream, WritableStreamDefaultWriter, WritableStreamDefaultController, and ReadableStream.pipeTo() are now supported (Firefox bug 1759597).

DOM

• Code can now use the static method AbortSignal.timeout(). This returns an AbortSignal that can be used to automatically abort an operation with TimeoutError after a specified time (Firefox bug 1753309).

WebAssembly

• WebAssembly now supports exceptions that can be thrown and caught in either WebAssembly or JavaScript (or some other runtime), crossing between the environment boundaries if not handled. The JavaScript representations of WebAssembly exceptions are WebAssembly.Exception and WebAssembly.Tag (Firefox bug 1759217).

WebDriver conformance (Marionette)

• Added support for user prompts (e.g., alert) on Android (Firefox bug 1708105).

Changes for add-on developers

• The color_scheme and content_color_scheme properties are added to theme manifest key and available in the theme API. These properties enable a theme to override whether a light or dark color scheme is automatically applied to the chrome or content (Firefox bug 1708105).
• You can now create a muted tab using tabs.create() with the new muted property in the createProperties object (Firefox bug 1372100).
• Support added for runtime.onSuspend and runtime.onSuspendCanceled improving support for event page features (Firefox bug 1753850).