Firefox 89 release notes for developers

This article provides information about the changes in Firefox 89 that will affect developers. Firefox 89 was released on June 1, 2021.

[!NOTE] See also Looking fine with Firefox 89 on Mozilla Hacks.

Changes for web developers

HTML

No changes.

CSS

• The {{cssxref("@media/forced-colors","forced-colors")}} media feature has been implemented (Firefox bug 1659511).
• The {{cssxref("@font-face/ascent-override", "ascent-override")}}, {{cssxref("@font-face/descent-override", "descent-override")}}, and {{cssxref("@font-face/line-gap-override", "line-gap-override")}} @font-face descriptors have been implemented (Firefox bug 1681691 and Firefox bug 1704494).
• The type() function for {{cssxref("image/image-set")}} has been implemented (Firefox bug 1695404).
• The {{cssxref("aspect-ratio")}} CSS property is now supported (Firefox bug 1672073).

JavaScript

• Top-level await is now enabled by default (Firefox bug 1681046).
• ArrayBuffers can now be created with a length greater than 2GB-1 (up to 8GB) on 64-bit systems (Firefox bug 1703505).

HTTP

No changes.

APIs

DOM

• {{domxref("PerformanceEventTiming")}} is now enabled by default (Firefox bug 1701029).
• The content of {{htmlelement("input")}} and {{htmlelement("textarea")}} elements can now be manipulated using {{domxref("Document.execCommand()")}} commands by default, preserving edit history and providing parity with other browsers, without contentEditable or any lengthy workarounds required (Firefox bug 1220696).

Removals

• The following sensor events and their associated handlers have been removed (primarily for better compatibility with other major browser engines, and to address concerns related to privacy leaks):
  • DeviceProximityEvent and its event handler window.ondeviceproximity (Firefox bug 1699707).
  • UserProximityEvent and its event handler window.onuserproximity) (Firefox bug 1699707).
  • DeviceLightEvent and its event handler window.ondevicelight (Firefox bug 1701824).

WebDriver conformance (Marionette)

Removals

• The rotatable capability that is not part of the WebDriver specification is no longer used (Firefox bug 1697630).

Changes for add-on developers

• Dynamic JS module imports are now working in WebExtension content scripts (Firefox bug 1536094).
• Extension resources listed in web_accessible_resources can be loaded regardless of the request's CORS mode (Firefox bug 1694679).
• Firefox's UI has been redesigned, which affects usage of the {{WebExtAPIRef("theme")}} API. The tab_background_separator and toolbar_field_separator properties are no longer supported. The tab_line and toolbar_vertical_separator will behave differently. For more information, see Changes to themeable areas of Firefox in version 89.
• The {{WebExtAPIRef("pageAction")}} button can no longer be pinned or unpinned from the address bar, because the three-dot meatball menu is no longer visible by default (Firefox bug 1691454). As a result, the pinned property of the page_action manifest key no longer has any effect (Firefox bug 1703537).
• The "Remove from Address Bar" context menu item has been removed from the {{WebExtAPIRef("pageAction")}} button (Firefox bug 1704474). For alternatives to this functionality, see Firefox bug 1712556.