Firefox 93 for developers

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 (Firefox bug 472823).
  • The default HTTP ACCEPT header for images changed to: image/avif,image/webp,*/* (following addition of support for the AVIF image format). (Firefox 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 (Firefox bug 1717760).

WebDriver conformance (Marionette)

Changes for add-on developers


  • Support for AVIF images is now enabled by default (Firefox 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