Mozilla has published initial details of what went wrong over the week-end when all add-ons were disabled due to the expiry of a certificate and what they did to quickly rectify the problem.
Discussion on Hacker News [ https://hacks.mozilla.org/2019/05/technical-details-on-the-recent-firefox-add-on-outage/ ]
Nice touch. Mozilla has also deleted Telemetry data for that period as some users had to enable Telemetry to get the hot-fix.
"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."
Some details on that in this companion post about the technical aspects of the outage
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