Firefox 91 for developers

This article provides information about the changes in Firefox 91 that will affect developers. Firefox 91 was released on August 10, 2021.

Note: See also Hopping on Firefox 91 on Mozilla Hacks.

Changes for web developers

HTML

No changes

CSS

Removals

JavaScript

HTTP

APIs

DOM

WebDriver conformance (Marionette)

  • Fixed a bug, which caused the commands WebDriver:AcceptAlert and WebDriver:DismissAlert to hang for user prompts as opened in a popup window (Firefox bug 1721982).
  • Fixed an inappropriate handling of the webSocketUrl capability, which would return true if webSocketUrl was not supported (Firefox bug 1713775).

Older versions