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 (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 (bug 1774589, bug 1787070).
  • CSS <calc-constant> type is implemented to allow for well-known constants such as pi and e within math functions (bug 1682444, 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 (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 (bug 1461589).


No notable changes



Media, WebRTC, and Web Audio

WebDriver conformance (WebDriver BiDi, Marionette)

WebDriver BiDi

  • Following a change in the specification, log entry level "warning" was renamed to "warn" (bug 1797115).
  • When using script.evaluate and script.callFunction with a sandbox name equal to an empty string, the evaluation will now be done using the default realm (bug 1793589).
  • Added support for the browsingContext.domContentLoaded event (bug 1756610).


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

Changes for add-on developers

  • Firefox now issues a warning when an extension is installed if its version number doesn't follow the recommended format (bug 1793925).

Older versions