Firefox 100 for developers

This article provides information about the changes in Firefox 100 that will affect developers. Firefox 100 was released on May 3, 2022.

Changes for web developers


No notable changes.


  • 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 (bug 1751217).


No notable changes.






  • 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 (bug 1759217).

WebDriver conformance (Marionette)

  • Added support for user prompts (e.g. alert) on Android (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 (bug 1708105).
  • You can now create a muted tab using tabs.create() with the new muted property in the createProperties object (bug 1372100).

Older versions