Firefox 88 release notes for developers

This article provides information about the changes in Firefox 88 that will affect developers. Firefox 88 was released on April 19, 2021.

[!NOTE] See also Never too late for Firefox 88 on Mozilla Hacks.

Changes for web developers

Developer Tools

• The toggle button for switching between raw and formatted response views has been implemented (Firefox bug 1693147). For examples, see Network request details > Response tab.

HTML

No changes.

CSS

• The {{cssxref(":user-valid")}} and {{cssxref(":user-invalid")}} pseudo-classes have been implemented (Firefox bug 1694141).
• The {{cssxref("image/image-set")}} functional notation is now enabled (Firefox bug 1698133), and was made available for {{cssxref("content")}} and {{cssxref("cursor")}} in Firefox bug 1695402 and Firefox bug 1695403.
• The default monospace font for macOS has been changed to Menlo (Firefox bug 1342741).
• The collapse value of {{cssxref("visibility")}} is now implemented for ruby annotations (Firefox bug 1697529).
• The alternate value for {{cssxref("ruby-position")}} has been implemented, and is the new initial value for the property (Firefox bug 1694748).
• The {{cssxref("outline")}} CSS property has been updated to follow the outline created by {{cssxref("border-radius")}}. As part of this work the non-standard -moz-outline-radius property has been removed. (Firefox bug 315209 and Firefox bug 1694146.)

Removals

• The {{cssxref(":-moz-submit-invalid")}} pseudo-class has been hidden behind a preference, thereby removing it from web content (Firefox bug 1694129).
• Default styling for the non-standard :-moz-ui-invalid and :-moz-ui-valid has been removed (Firefox bug 1693969).

JavaScript

• Added support for RegExp match indices (Firefox bug 1519483).
• Intl.DisplayNames() and Intl.ListFormat() now have stricter checking that options passed to the constructor are objects, and will throw an exception if a string or other primitive is used instead (Firefox bug 1696881).

HTTP

• FTP has been disabled on all releases (preference network.ftp.enabled now defaults to false), with the intent of removing it altogether in Firefox 90 (Firefox bug 1691890). Complementing this change, the extension setting browserSettings.ftpProtocolEnabled has been made read-only, and web extensions can now register themselves as protocol handlers for FTP (Firefox bug 1626365).

Security

No changes.

APIs

DOM

• Code can now use the new static method AbortSignal.abort() to return an {{domxref("AbortSignal")}} that is already set as aborted (Firefox bug 1698468).

WebDriver conformance (Marionette)

• Marionette will no longer be enabled unless the --marionette command line argument or the MOZ_MARIONETTE environment variable is specified. As such the marionette.enabled preference is no longer used. With this change the state of navigator.webdriver now correctly reflects the enabled state of Marionette (Firefox bug 1593343).
• Fixed a bug where pointer actions other than down and up inappropriately led to buttons being pressed (Firefox bug 1686361).
• Fixed a race condition in WebDriver:GetCurrentURL that could have led the command to return the URL of the previously opened page, or even a hang in Marionette (Firefox bug 1664881).

Changes for add-on developers

• url can now be used to limit the properties for which the {{WebExtAPIRef("tabs.onUpdated")}} event is triggered (Firefox bug 1680279).