Firefox 84



This article provides information about the changes in Firefox 84 that will affect developers. Firefox 84 was released on December 15, 2020.

Note: See also And now for … Firefox 84 on Mozilla Hacks.

The information on this page is only about version 84.0 of Mozilla Firefox 84.0 (x86 tr). How to erase Mozilla Firefox 84.0 (x86 tr) from your computer with the help of Advanced Uninstaller PRO Mozilla Firefox 84.0 (x86 tr) is a program released by the software company Mozilla. Sometimes, computer users choose to erase it. Firefox 84 for developers This article provides information about the changes in Firefox 84 that will affect developers. Firefox 84 was released on December 15, 2020. Note: See also And now for.

Changes for web developers

Developer Tools

  • The Firefox Accessibility Inspector now supports displaying the keyboard tab order on a web page. This provides a better high-level overview of how the page will be navigated using the keyboard than tabbing through the links (bug 1654956).

Firefox Beta 84

HTML

CSS

  • We've added support for complex selectors to the :not pseudo-class (bug 933562).

Removals

  • We've removed the proprietary -moz-default-appearance property values scrollbar-small (scrollbar-width: thin is used instead) and scrollbar (macOS only; scrollbar-horizontal and scrollbar-vertical are used instead) (bug 1673132).

JavaScript

Firefox
  • Custom date/time formats specified as options to the Intl.DateTimeFormat() constructor can now include fractionalSecondDigits — the number of digits used to represent fractions of a second (bug 1645107).

HTTP

Security

  • Firefox now ensures that localhost URLs — such as http://localhost/ and http://dev.localhost/ — refer to the local host's loopback interface (e.g. http://127.0.0.1). As a result, resources loaded from localhost are now assumed to have been delivered securely (see Secure contexts), and also will not be treated as mixed content (bug 1220810, bug 1488740).

APIs

Firefox 84 Crashing

  • We've added support for the PerformancePaintTiming interface of the Paint Timing API (bug 1518999).
  • The Navigator.registerProtocolHandler() method now only accepts two parameters: scheme and url. title has been removed (bug 1631464).

Media, WebRTC, and Web Audio

  • The MediaRecorder.start() method now throws an InvalidModificationError if the number of tracks on the stream being recorded has changed (bug 1581139).

Removals

  • The application cache has been removed — developers should use the Service Worker API instead (bug 1619673).

Firefox 84 Download

WebAssembly

WebDriver conformance (Marionette)

  • Added chrome scope support for WebDriver:PerformActions and WebDriver:ReleaseActions (bug 1365886).
  • The new Fission-compatible API has been enabled by default now. To revert to the former API the marionette.actors.enabled preference has to be set to false (bug 1669169).
  • Fixed WebDriver:SwitchToWindow to always switch back to the top-level browsing context (bug 1305822).
  • Improved browsing context checks for WebDriver:SwitchToParentFrame (bug 1671622).
  • Fixed a hang for WebDriver:Back encountered when the currently-selected <iframe> gets unloaded (bug 1672758).

Known bugs

  • After page navigation, accessing a previously-retrieved element might not always raise a 'stale element' error, and can also lead to a 'no such element' error. To prevent this, set the marionette.actors.enabled preference to false (bug 1684827).

Changes for add-on developers

Firefox 84
  • The browsingData.remove() API now supports removing a subset of data types by cookieStoreId.

Older versions

Firefox 84.0.2 Download

With the release of Firefox 84, we are pleased to welcome the developers who’ve contributed their first code change to Firefox, 10 of whom were first-time contributors to the code. Please join us in thanking each of these diligent and enthusiastic individuals, and take a look at their contributions:

Firefox 84 Enable Flash

  • h20190017-pilani.ac.in: 1663884
  • paulkrznaric: 1669832
  • Andrey Bienkowski: 1673934, 1674425, 1674635, 1674841, 1674971, 1674980, 1674986, 1675094, 1675299, 1675925
  • Chris GAUDRY: 1675037
  • NAMAN JAIN: 1671080, 1673051
  • Nerixyz: 1674577
  • Seun: 1671163
  • Sunita Sen: 1666340, 1669027, 1677302
  • William Immendorf: 1643243
  • jsal: 1662985