Firefox 108 for 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

• Content-Security-Policy HTTP header directives style-src-elem and style-src-attr are now supported. A server can use these to specify valid sources for stylesheet <style> elements and <link> elements with rel="stylesheet", and for styles applied to individual elements, respectively (Firefox bug 1529338).
• Content-Security-Policy HTTP header directives script-src-elem and script-src-attr are now supported. A server can use these to specify valid sources for JavaScript <script> elements, and for inline script event handlers like onclick, respectively (Firefox bug 1529337).
• Content-Security-Policy violation reports now include effective-directive and status-code properties. For more information, see Violation report syntax (Firefox bug 1192684).

• Import maps are now supported. Import maps provide flexibility and additional control over how browsers resolve module specifiers when importing JavaScript modules. (Firefox bug 1795647).

Media, WebRTC, and Web Audio

• The Web MIDI API is now available in secure contexts. Calls to navigator.requestMIDIAccess() will prompt users with active MIDI devices to install a Site Permission Add-On, which is required to enable the API. For more information see Firefox bug 1795025.

WebDriver BiDi

• Following a change in the specification, log entry level "warning" was renamed to "warn" (Firefox 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 (Firefox bug 1793589).
• Added support for the browsingContext.domContentLoaded event (Firefox bug 1756610).

Marionette

• 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).

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