Firefox 75 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


  • The loading attribute of the <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 (bug 1542784).
  • The value of the <style> element's type attribute is now restricted to text/css only, as per the spec (bug 1614329).



The new roles and objects related to ARIA annotations 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):

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.




  • The HTMLFormElement interface has a new method, requestSubmit(). Unlike the old (and still available) 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 submit event is delivered and the form is checked for validity prior to the data being submitted (bug 1613360).
  • The submit event is now represented by an object of type SubmitEvent rather than a simple Event. SubmitEvent includes a new submitter property, which is the 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 (bug 1588715).
  • Calling the 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 (bug 1610821).

Web animations API

Firefox 75 sees numerous additions to the Web Animations API:

Media, Web Audio, and WebRTC


No changes.


  • CSP 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 (bug 1374612).


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 (bug 1622012).
  • Fixed WebDriver:Print to no longer add extra margins to the document (bug 1616932).
  • Changed the preference value for network.http.speculative-parallel-limit to 0, to no longer force-disable speculative connections (bug 1617869).


No changes.

Changes for add-on developers

API changes

Manifest changes

Older versions