Mozilla Firefox Developer Version

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Warning: Firefox now includes downgrade protection to prevent corruption of user profile data. If you install an older version, you'll be prompted to create a new Firefox profile.

If there is a problem with a new version of Firefox, some people may want to downgrade Firefox to a previous version but we do not recommend this. The latest Firefox version includes security updates so downgrading to an older version leaves you more vulnerable to attacks and usually doesn't fix the problem. This article gives you some alternatives to downgrading and links to older versions of Firefox if you do choose to downgrade.

  1. Delete the Mozilla Firefox Folders in C:Program Files and C:Program Files(x86) Then restart system. Then run Windows Disk Cleanup. Then run it again and click the button that says Cleanup System Files. Note: your Firefox Profile is saved. (if not wanting bookmarks.
  2. The developer release will install alongside a standard Firefox Portable install in a FirefoxPortableDeveloper directory. Note that PortableApps.com will release one version for each major version (example: 78b1 but not 78b2). For updates within each major release, use the internal updater.

Table of Contents

Problems with an update are usually not caused by the new version of Firefox, but rather the update process. In most cases, installing a previous version will not help. Instead, see:

The browser we know as Firefox started as Phoenix 0.1 in Sept 2002. Due to Phoenix Bios existing Mozilla changed name to Firebird for 0.6 to 0.7. Then due to the open source Firebird SQL already being around for a bit Mozilla decided to not have confusion between the two and changed it to Firefox starting at Release version 0.8 to present.

Note: Other problems can be solved with the Refresh Firefox feature. It restores Firefox to its default state while saving your essential information.

Ensure all security and security-related software is fully updated. Some security software will need to be upgraded to a new version so that it is compatible with each Firefox version update.

Optional software bundled with security software also may need updating. Such software may not be essential for your security but, if outdated, may interfere with the use of Firefox or cause Firefox to crash.

If you still want to downgrade, you can visit Mozilla's directory of older Firefox versions using the links below. Please note, however, that using older versions can make Firefox insecure and more vulnerable to attacks and scams. We recommend that you always use the newest version of Firefox.
Warning: Old Firefox versions pose a significant security risk.
  • Firefox 77.0.132-bit (US English)
  • Firefox 77.0.164-bit (US English)
  • Firefox 77.0.132-bit (US English)
  • Firefox 77.0.164-bit (US English)
  • Firefox 78.0.232-bit (US English)
  • Firefox 78.0.264-bit (US English)
  • Firefox 78.0.232-bit (US English)
  • Firefox 78.0.264-bit (US English)
  • Firefox 79.032-bit (US English)
  • Firefox 79.064-bit (US English)
  • Firefox 79.032-bit (US English)
  • Firefox 79.064-bit (US English)
  • Firefox 80.0.132-bit (US English)
  • Firefox 80.0.164-bit (US English)
  • Firefox 80.0.132-bit (US English)
  • Firefox 80.0.164-bit (US English)
  • Firefox 81.0.232-bit (US English)
  • Firefox 81.0.264-bit (US English)
  • Firefox 81.0.232-bit (US English)
  • Firefox 81.0.264-bit (US English)
  • Firefox 82.0.332-bit (US English)
  • Firefox 82.0.364-bit (US English)
  • Firefox 82.0.332-bit (US English)
  • Firefox 82.0.364-bit (US English)
  • Firefox 83.032-bit (US English)
  • Firefox 83.064-bit (US English)
  • Firefox 83.032-bit (US English)
  • Firefox 83.064-bit (US English)
  • Firefox 84.0.232-bit (US English)
  • Firefox 84.0.264-bit (US English)
  • Firefox 84.0.232-bit (US English)
  • Firefox 84.0.264-bit (US English)
  • Firefox 85.0.232-bit (US English)
  • Firefox 85.0.264-bit (US English)
  • Firefox 85.0.232-bit (US English)
  • Firefox 85.0.264-bit (US English)
  • Firefox 86.0.132-bit (US English)
  • Firefox 86.0.164-bit (US English)
  • Firefox 86.0.132-bit (US English)
  • Firefox 86.0.164-bit (US English)
  • Firefox 87.032-bit (US English)
  • Firefox 87.064-bit (US English)
  • Firefox 87.032-bit (US English)
  • Firefox 87.064-bit (US English)
Important: By default, Firefox is set for automatic updates. To prevent Firefox from automatically updating itself after you install an older version, you'll need to change your Firefox update settings: In the Menu bar at the top of the screen, click Firefox and select Preferences.Click the menu button and select ... In the General panel, go to the Firefox Updates section.

Instead of downgrading to an older, insecure version of Firefox and changing your update settings, you should consider these alternatives:

Install Firefox Extended Support Release.Firefox Extended Support Release (ESR) is an official version of Firefox developed for large organizations such as universities and businesses. Firefox ESR does not come with the latest features, but it does have the latest security and stability fixes. For more information, see the article Switch to Firefox Extended Support Release (ESR) for personal use.

Use the latest version of another browser. If you are not satisfied with the current Firefox version or it simply is not working right now, there are alternative browsers that you can use to browse the web.

Edition

This article provides information about the changes in Firefox 85 that will affect developers. Firefox 85 was released on January 26, 2021.

Note: See also January brings us Firefox 85 on Mozilla Hacks.

Changes for web developers

Developer Tools

  • Developers can now use the Page Inspector to toggle the :focus-visible pseudo-class for the currently selected element (in addition to the pseudo classes that were previously supported: :hover, :active and :focus, :focus-within, and :visited). (bug 1617608).

HTML

  • <link> is now enabled. (bug 1626997).

Removals

  • The <menuitem> HTML element is no longer available — it has been hidden behind the dom.menuitem.enabled flag. (bug 1680596).

CSS

  • The :focus-visible pseudo-class is now enabled. (bug 1445482).
  • The pinch-zoom value for the touch-action property is now enabled. (bug 1329241).

JavaScript

  • The collation property can now be specified in the options passed to the Intl.Collator() constructor (bug 1670062). This allows developers to write code with greater clarity:

Plugins

Download Mozilla Firefox Developer Version

  • Flash support has been completely removed from Firefox (bug 1675349). Read our plugin roadmap for more information.
Mozilla firefox developer edition download filehippo

APIs

WebDriver conformance (Marionette)

  • Fixed a potential page load timeout situation when WebDriver:ElementClick is called for a link with a target other than _blank (bug 1678455).
  • Using web element references on browsing contexts other than the originating one now correctly returns a no such element error instead of a stale element reference error (bug 1684827).

Known bugs

Mozilla Firefox Developer Edition Portable

  • WebDriver commands following a call to WebDriver:SwitchToFrame can fail with a 'no such window' error if the frame's content hasn't yet finished loading (bug 1691348).
  • After a cross-group 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 1690308).

Mozilla Firefox Developer Edition Vs Regular

Changes for add-on developers

Mozilla Firefox Versions List

Older versions