Firefox 75 release notes for developers

This article provides information about the changes in Firefox 75 that will affect developers. Firefox 75 was released on April 7, 2020.

See also the accompanying hacks post — Firefox 75: Ambitions for April.

Changes for web developers

Developer tools

• It is now possible to resize the rectangle of the Measuring Tool (Firefox bug 1152321).
• In the inspector, you can now use XPath expressions to locate elements, in addition to locating elements using CSS selectors as before (Firefox bug 963933).
• You can now filter WebSocket messages using regular expressions, in addition to plain text search, by writing the regular expression in slashes (Firefox bug 1593837).

HTML

• The loading attribute of the {{HTMLElement("img")}} element has now been implemented. This string value can be used to specify that the image should be lazily loaded, by setting its value to lazy (Firefox bug 1542784).
• The value of the <style> element's type attribute is now restricted to text/css only, as per the spec (Firefox bug 1614329).

CSS

• Support for the {{cssxref("min", "min()")}}, {{cssxref("max", "max()")}}, and {{cssxref("clamp", "clamp()")}} functions has been implemented (Firefox bug 1519519).
• The all value of the {{cssxref("text-decoration-skip-ink")}} property has been added (Firefox bug 1611965)

Accessibility

New ARIA roles and attributes are now exposed in Firefox, on Windows and Linux (bear in mind that these still won't be usable until screen readers start to support them):

• aria-description (Firefox bug 1608961).
• role="mark" and role="suggestion" (Firefox bug 1608965).
• role="comment" (Firefox bug 1608969).
• Multiple IDs on aria-details (Firefox bug 1608883).

[!NOTE] On macOS, we are first waiting for Apple to define what Safari will expose as Apple-dialect attributes to VoiceOver, and will then follow suit.

JavaScript

• Public static class fields are now supported (Firefox bug 1535804).
• The Intl.Locale class is now supported (Firefox bug 1613713).
• The Function.caller property has been updated to be aligned with the latest ECMAScript spec proposal. Previously throwing a TypeError, it now returns null if the caller is a strict, async, or generator function (Firefox bug 1610206).

APIs

DOM

• The {{domxref("HTMLFormElement")}} interface has a new method, {{domxref("HTMLFormElement.requestSubmit", "requestSubmit()")}}. Unlike the old (and still available) {{domxref("HTMLFormElement.submit", "submit()")}} method, requestSubmit() acts as if a specified submit button has been clicked, rather than just sending the form data to the recipient. Thus the {{domxref("HTMLFormElement.submit_event", "submit")}} event is delivered and the form is checked for validity prior to the data being submitted (Firefox bug 1613360).
• The {{domxref("HTMLFormElement.submit_event", "submit")}} event is now represented by an object of type {{domxref("SubmitEvent")}} rather than a simple {{domxref("Event")}}. SubmitEvent includes a new {{domxref("SubmitEvent.submitter", "submitter")}} property, which is the {{domxref("Element")}} that was invoked to trigger the form submission. With this event, you can have a single handler for submit events that can discern which of multiple submit buttons or links was used to submit the form (Firefox bug 1588715).
• Calling the {{domxref("HTMLElement.click", "click()")}} method on a detached element (one not part of a DOM tree) now functions normally, leading to a click event being sent to it (Firefox bug 1610821).

Web animations API

Firefox 75 sees numerous additions to the Web Animations API:

• Implicit to/from keyframes are now supported, as is automatically removing filling animations that have been replaced by other indefinitely filling animations (Firefox bug 1618773). This includes enabling of support for:

  • Animation.commitStyles()
  • Animation.onremove
  • Animation.persist()
  • Animation.replaceState

• The Animation.timeline getter, Document.timeline, DocumentTimeline, and AnimationTimeline features are now enabled by default (Firefox bug 1619178).

• The Document.getAnimations() and Element.getAnimations() methods are now enabled by default (Firefox bug 1619821).

Media, Web Audio, and WebRTC

• The RTCPeerConnection.setLocalDescription() method can now be called without arguments, in which case the WebRTC runtime will try to create the new local session description itself (Firefox bug 1568292).

HTTP

No changes.

Security

• CSP {{Glossary("Nonce", "nonces")}} from non-script sources, such as CSS selectors, and .getAttribute("nonce") calls, are now hidden. Instead, check the .nonce property to access nonces from scripts (Firefox bug 1374612).

Plugins

No changes.

WebDriver conformance (Marionette)

• Fixed a bug that always caused Marionette to initialize when Firefox starts-up. It has been limited to the command line argument and environment variable now (Firefox bug 1622012).
• Fixed WebDriver:Print to no longer add extra margins to the document (Firefox bug 1616932).
• Changed the preference value for network.http.speculative-parallel-limit to 0, to no longer force-disable speculative connections (Firefox bug 1617869).

Other

No changes.

Changes for add-on developers

API changes

• We've added some new settings in {{WebExtAPIRef("browserSettings")}} (Firefox bug 1286953):

  • {{WebExtAPIRef("browserSettings.zoomSiteSpecific")}} to control whether zooming is on a per-site or per-tab basis
  • {{WebExtAPIRef("browserSettings.zoomFullPage")}} to control whether zoom is applied to the entire page or to text only.

• The name of the file used when saving a PDF with {{WebExtAPIRef("tabs.saveAsPDF")}} can be specified using toFileName in the type tabs.PageSettings.(Firefox bug 1483590)

Manifest changes

• The "privacy" permission is now optional. (Firefox bug 1618399)