Mozilla has decided to delete all telemetry, or user's usage and performance data, that was collected by Firefox while they were rolling out the study to fix disabled Firefox addons.

On May 4 at 1:00 AM UTC a certificate used to sign Firefox addons expired. As the browser requires all addons to have a valid signature, Firefox disabled all the addons when the certificate expired.

As a way to fix this, Mozilla released a system extension in the form of a Study called "hotfix-update-xpi-signing-intermediate-bug-1548973" that would be distributed to all users who have studies enabled. For many people, this was a problem as you needed to allow usage data to be uploaded to Mozilla in order to enable the studies.

Ultimately, Mozilla released Firefox 66.0.4 and then Firefox 66.0.5 to resolve the issues with the expired certificate without the need for a study, but for many it was too late as they had already enabled studies in the browser.

Mozilla wants to atone

As a way of apologizing and making good to everyone who enabled studies and thus enabled telemetry, Mozilla has decided to delete the telemetry data for all Firefox users that was collected during the period that the fix was deployed.

"In order to address this issue as quickly as possible, we used our “Studies” system to deploy the initial fix, which requires users to be opted in to Telemetry," stated a blog post by Mozilla. "Some users who had opted out of Telemetry opted back in, in order to get the initial fix as soon as possible. As we announced in the Firefox Add-ons blog at 2019-05-08T23:28:00Z there is now no longer a need to have Studies on to receive updates anymore; please check that your settings match your personal preferences before we re-enable Studies, which will happen sometime after 2019-05-13T16:00:00Z. In order to respect our users’ potential intentions as much as possible, based on our current set up, we will be deleting all of our source Telemetry and Studies data for our entire user population collected between 2019-05-04T11:00:00Z and 2019-05-11T11:00:00Z."

To make it clearer to understand, at least for us in the USA, this means Mozilla will delete all performance and usage data for the entire Firefox population that was collected between May 5th at 6:00 AM EST and May 11th at 6:00 AM EST.

They also want to stress, that if you do not want your telemetry data to be uploaded to Mozilla, you can disable it in Firefox as studies are no longer needed.

To disable studies and telemetry, go to Firefox Preferences -> Privacy & Security and uncheck Allow Firefox to send technical and interaction data to Mozilla as shown below..

Telemetry Disabled

Once you uncheck that option, both studies and telemetry will be disabled in Firefox.