Firefox 108 for developers

This article provides information about the changes in Firefox 108 that will affect developers. Firefox 108 was released on December 13, 2022.

Changes for web developers


  • The <source> element supports height & width attributes when it is a child of a <picture> element. This functionality can be configured via the dom.picture_source_dimension_attributes.enabled preference which is now set to true by default (Firefox bug 1795953).


  • Trigonometric functions are now enabled with the layout.css.trig.enabled preference set to true by default. This allows the use of sin(), cos(), tan(), asin(), acos(), atan(), and atan2() functions (Firefox bug 1774589, Firefox bug 1787070).
  • CSS <calc-constant> type is implemented to allow for well-known constants such as pi and e within math functions (Firefox bug 1682444, Firefox bug 1787070).
  • Container query length units are now supported via the layout.css.container-queries.enabled preference, which is set to false by default. Setting this preference to true allows the use of cqw, cqh, cqi, cqb, cqmin, and cqmax units of length which are relative to the size of a query container. For more information on these units, see the CSS Container Queries documentation (Firefox bug 1744231).
  • The font-variant-emoji property is now supported via the layout.css.font-variant-emoji.enabled preference, which is set to false by default. This property allows you to set a default presentation style for displaying emojis (Firefox bug 1461589).


No notable changes



Media, WebRTC, and Web Audio

WebDriver conformance (WebDriver BiDi, Marionette)

WebDriver BiDi


  • Added support for the tiltX, tiltY and twist properties of pointer actions for WebDriver:PerformActions (Firefox bug 1793832).
  • Fixed a bug where WebDriver:GetElementText wasn't returning the element text for pretty-printed XML (Firefox bug 1794099).
  • HTMLDocument is no longer serialized as a WebElement reference (Firefox bug 1793920).
  • WebDriver:NewWindow now opens a window with an about:blank tab instead of about:newtab (Firefox bug 1533058).

Changes for add-on developers

Older versions