Firefox 93 for developers

Draft: This page is not complete.

This article provides information about the changes in Firefox 93 that will affect developers. Firefox 93 was released on October 5, 2021.

Note: See also Lots to see in Firefox 93 on Mozilla Hacks.

Changes for web developers





  • The SHA-256 algorithm is now supported for HTTP Authentication using digests. This allows much more secure authentication than previously available using the MD5 algorithm (bug 1682995).
  • The default HTTP ACCEPT header for images changed to: image/avif,image/webp,*/* (following addition of support for the AVIF image format). (bug 1682995).




  • KeyboardEvent.initKeyEvent() has been moved behind the preference dom.keyboardevent.init_key_event.enabled and is disabled by default. The method is not present in any current specification or supported in other current browsers (bug 1717760).

WebDriver conformance (Marionette)

  • Fixed a bug which caused WebDriver:Print to fail for large documents (bug 1721982).

Changes for add-on developers


  • Support for AVIF images is now enabled by default (bug 1682995). This format has excellent compression and no patent restrictions (it was developed by the Alliance for Open Media). Firefox can display still images, with colorspace support for both full and limited range colors, and image transforms for mirroring and rotation. The preference image.avif.compliance_strictness can be used to adjust the compliance strictness with the specification. Animated images are not supported.

Older versions