On late Friday, May 3rd, 2019, we became aware of an issue with Firefox that prevented existing and new add-ons from running or being installed. We are very sorry for the inconvenience caused to people who use Firefox.

A fix has been released in Firefox version 66.0.4. An update will be rolled out automatically with the latest fixes or you can download a new version:

• Firefox desktop
• Firefox for Android on Google Play (or see your device's app download site).

Please see the 66.0.4 release notes for more information.

Known issues and workarounds

Add-ons appearing as unsupported or disappeared from your about:addons page.

Their data is not lost because it is stored locally on your profile directory. (Bug 1549129). Re-installing the add-ons will recover the data:

1. Go to https://addons.mozilla.org/firefox/.
2. Search for your add-ons and install them individually.

Master password

If you have a master password that has not been used for a while, the fix in 66.0.4 might not take effect. You can work around this by entering or resetting your master password.

If you know your master password:

1. Click the menu button and choose Options.Preferences.
2. Select the Privacy & Security panel.
3. Under Logins and Passwords section, click on Saved logins…. This will prompt for your master password.
4. After you have entered your master password successfully, restart Firefox.

If you don’t know your master password:

1. Follow the instructions at Reset your Master Password if you've forgotten it.
2. Once you have reset the master password, Firefox will restart.

Container add-ons

Containers add-ons may reset to their default state. If add-ons that use the Containers functionality, like Multi-Account Containers and Facebook Container, were disabled as part of this problem, any lost site data for containers, as well as deleted custom containers you may have configured, will not be recovered by this new release.

Data that may be lost for Container add-ons include configuration data, for which containers to enable or disable, and container names and icons. Locally-stored data for the container (cookies and permissions) are also affected. See Bug 1549204.

See Multi-Account Containers to set them up again.

Themes will need to be re-enabled

Settings for themes will default back and will need to be re-enabled:

1. Visit https://addons.mozilla.org/firefox/themes/.
2. Click on the theme you want to install.
3. Click the Install theme button. Click Remove if you change your mind. Your changes will apply automatically.

See Use themes to change the look of Firefox or Built-in themes in Firefox - alternative to complete themes to learn more about themes.

Home page and search

If your home page or search settings are set by an add-on, they will be reset to their default settings (Bug 1549192) To change them back:

Home page

1. Click the menu button and choose Options.Preferences.
2. Select the Home panel.
3. Choose your desired settings for the Home page and new windows and New tabs by clicking the drop-down menu next to each one.

See How to set the home page for more.

Search

1. Click the menu button and choose Options.Preferences.
2. Select the Search panel.
3. Choose a default search engine and additional search engines.

See Change your default search settings in Firefox for more information.