Late on Friday May 3rd, 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.

Our team has identified and rolled-out a fix for all Firefox Desktop users on Release, Beta and Nightly. The fix will be automatically applied in the background within the next few hours. No active steps need to be taken to make add-ons work again.

To provide this fix on short notice, we are using the Studies system. This system is enabled by default, and no action is needed unless Studies have been disabled. Firefox users can check if they have Studies enabled by going to:

• Firefox Options/Preferences -> Privacy & Security -> Allow Firefox to install and run studies (scroll down to find the setting)

• Studies can be disabled again after the add-ons have been re-enabled

It may take up to six hours for the Study to be applied to Firefox. To check if the fix has been applied, you can enter “about:studies” in the location bar. If the fix is active, you’ll see “hotfix-update-xpi-signing-intermediate-bug-1548973” as follows:

You may also see “hotfix-reset-xpi-verification-timestamp-1548973” listed, which is part of the fix and may be in the Active studies or Completed studies section(s).

We are working on a general fix that doesn’t use the Studies system and will keep this blog post updated accordingly.

We’ll continue to provide updates on continued efforts on this post, and will share a more substantial update in the coming days.