Firefox 96 for developers

This article provides information about the changes in Firefox 96 that affect developers. Firefox 96 was released on January 11, 2022.

Changes for web developers


No notable changes


  • The hwb() function for use as a CSS color value has been implemented. The hwb() functional notation expresses a given color according to its hue, whiteness, and blackness. An optional alpha component represents the color's transparency. (bug 1352755).
  • Firefox now provides support for the color-scheme property. This allows an element to indicate which color schemes it can comfortably be rendered in. Common options include "light" and "dark", or "day mode" and "night mode". (bug 1576289).
  • The counter-reset property now supports the reversed() function for creating reversed CSS counters, which are intended for numbering elements in descending order. This can be used with the list-item counter to automatically number ordered lists in reverse order, starting from the number of elements in the list (list-item is a counter that is automatically applied for ordered lists, such as those created using <ol>). Firefox uses this feature internally to support the <ol> reversed attribute. (bug 1706346).


No notable changes.


  • Cookies sent from the same domain but using different schemes (for example http or https) are now considered to be from different sites with respect to the cookie SameSite directive. In addition, cookies are assumed to implicitly set SameSite=Lax if the SameSite attribute is not specified (previously the default was SameSite=None), and cookies with SameSite=None require a secure context. (bug 1617609).




  • The IntersectionObserver() constructor now sets the default rootMargin if an empty string is passed in the associated parameter option, instead of throwing an exception (bug 1738791).

Media, WebRTC, and Web Audio

  • A number of deprecated non-standard statistics fields have been removed from the WebRTC Statistics API, including: bitrateMean, bitrateStdDev, framerateMean, framerateStdDev, and droppedFrames. (bug 1367562).

WebDriver conformance (Marionette)

  • Added the command WebDriver:GetElementShadowRoot to retrieve the shadow root (open or closed) hosted by a given element (bug 1700073).
  • Fixed a bug in WebDriver:ExecuteScript and WebDriver:ExecuteAsyncScript that caused a cyclic object value error when trying to return the ShadowRoot of an element (bug 1489490).
  • WebDriver:Print has been enhanced to support page ranges when printing documents as PDF (bug 1678347).

Changes for add-on developers

Older versions