Firefox 106 for developers

• The <source> element now supports height & width attributes when it is a child of a <picture> element. This functionality is an experimental feature enabled using the dom.picture_source_dimension_attributes.enabled preference (Firefox bug 1694741).

• The <semantics> and <maction> MathML elements now only render the first child element by default (Firefox bug 1588733).

• The @supports at-rule now supports the font-tech() and font-format() functions. These functions can be used to test whether a browser supports a given font technology or format and CSS styles can be applied based on the result (Firefox bug 1786493).

No notable changes.

DOM

• The HTMLMetaElement.media property is now supported. This property enables you to set different theme colors based on media values (e.g. max-width: 600px). Meta elements with media properties allow the browser to use the content value in conjunction with theme-color to set the page or UI colors for a given media query (Firefox bug 1706179).

WebDriver BiDi

• Added basic support for the script.getRealms command that is currently limited to the WindowRealmInfo type which includes window realms and sandbox realms (Firefox bug 1766240).
• Added support for the browsingContext.load event, which is emitted when a load event is triggered on a BrowsingContext's window (Firefox bug 1756619).
• Added an object reference store to hold strong references for serialized remote values (Firefox bug 1770736).
• Added support for de-serializing remote references created in the object reference store (Firefox bug 1788124).
• Added full support for the script.evaluate, script.callFunction and script.disown commands (Firefox bug 1778976).

Marionette

• Added support for wheel input source for Actions, which is associated with a wheel-type input device (Firefox bug 1746601).
• Added support for opening and closing tabs in GeckoView based applications (eg. Firefox for Android) (Firefox bug 1506782).

• The ability to set the "background" manifest key property "persistent" to false for Manifest V2 (to make a background page non-persistent) is now available by default.
• The object-src directive in the "content_security_policy" manifest key is now optional (Firefox bug 1766881). See object-src directive on the "content_security_policy" manifest key page for more details.