Firefox 87 for developers

• Developers can now use the Page Inspector to simulate prefers-color-scheme media queries, without having to change the operating system to light or dark mode (Firefox bug 1679408 and Firefox bug 1692272).
• Developers can now use the Page Inspector to toggle the :target pseudo-class for the currently selected element in addition to the pseudo-classes that were previously supported: :hover, :active and :focus, :focus-within, :focus-visible, and :visited (Firefox bug 1689899).
• Firefox 87 sees a number of Page Inspector improvements and bug fixes related to inactive CSS rules:
  • The table-layout property is now marked as inactive for non-table elements (Firefox bug 1551571).
  • The scroll-padding properties (shorthand and longhand) are now marked as inactive for non-scrollable elements (Firefox bug 1551577).
  • The text-overflow property was previously incorrectly marked as inactive for some overflow values (Firefox bug 1671457).

No changes.

• Some languages have digraphs that are always capitalized together, for example IJ in Dutch. The ::first-letter pseudo-element now respects these digraphs and treats them as a single unit (Firefox bug 92176).
• The <link> element is no longer matched by :link, :visited, or :any-link. This aligns the behavior in Firefox to existing behavior in Chrome and to a recent spec change (Firefox bug 1687538).

Removals

• The following Firefox-specific theme-related media features have been disabled for use in web pages (Firefox bug 787521):
  • -moz-mac-graphite-theme
  • -moz-mac-lion-theme
  • -moz-maemo-classic
  • -moz-windows-classic
  • -moz-windows-compositor
  • -moz-windows-default-theme
  • -moz-windows-theme
  • -moz-scrollbar-end-backward
  • -moz-scrollbar-end-forward
  • -moz-scrollbar-start-backward
  • -moz-scrollbar-start-forward
  • -moz-scrollbar-thumb-proportional
  • -moz-menubar-drag
• The non-standard values of caption-side (left, right, top-outside, and bottom-outside) have been removed and placed behind the layout.css.caption-side-non-standard.enabled flag (Firefox bug 1688695).

No changes.

• Some enterprise authentication services require that TLS client certificates be sent in CORS preflight requests. Users of these services can enable this (non-specification compliant) behavior using the network.cors_preflight.allow_client_cert preference (Firefox bug 1511151).
• The default Referrer-Policy has been changed to strict-origin-when-cross-origin (from no-referrer-when-downgrade), reducing the risk of leaking referrer information in cross-origin requests (Firefox bug 1589074).
• Content-Length has been added to the list of CORS-safelisted response headers (Firefox bug 1460299).

No changes.

DOM

• The beforeinput event and getTargetRanges() method are now enabled by default. They allow web apps to override text edit behavior before the browser modifies the DOM tree, and provide more control over input events to improve performance. The global beforeinput event is sent to an <input> element — or any element whose contenteditable attribute is set to true — immediately before the element's value changes. The getTargetRanges() method of the InputEvent interface returns an array of static ranges that will be affected by a change to the DOM if the input event is not canceled.

• The work of rewriting Marionette to support Fission (site-isolation) has been finished, so the old Marionette implementation has been removed. The marionette.actors.enabled preference, which toggled between the new and old implementations, has therefore also been removed (Firefox bug 1669172).
• WebDriver commands following a call to WebDriver:SwitchToFrame will no longer fail with a "no such window" error if the frame's content hasn't yet finished loading (Firefox bug 1691348).
• After a cross-group page navigation, accessing a previously-retrieved element will now always raise a "stale element" error; there is no longer a chance that this action will lead to a "no such element" error (Firefox bug 1690308).
• Addon:Uninstall now raises an unknown error when the id of the add-on to uninstall is unknown (Firefox bug 1693022).

• nativeMessaging is now an optional permission (Firefox bug 1630415).
• Added support for querying and setting color management related features with browserSettings.colorManagement (Firefox bug 1719688) and (Firefox bug 1714428).