Eric Rescorla has a blog post over at Mozilla about the technical details on the recent Firefox add-on outage. He covers the background of how they use certificates, how they tried to mitigate the damage from the outage, how they worked to solve the problem without breaking more things, deployment of the replacement certificate, and why it took so long to fix.
Recently, Firefox had an incident in which most add-ons stopped working. This was due to an error on our end: we let one of the certificates used to sign add-ons expire which had the effect of disabling the vast majority of add-ons. Now that we've fixed the problem for most users and most people's add-ons are restored, I wanted to walk through the details of what happened, why, and how we repaired it.
There were a lot of work arounds discussed here and elsewhere, some of them quite stupid so, lastly, remember to undo any temporary work-arounds that might have been deployed last weekend.
Earlier on SN: In Firefox All Extensions Disabled Due to Expiration of Intermediate Signing Cert
(Score: 2, Informative) by bolek_b on Saturday May 11 2019, @05:44AM
This week I had to migrate 80% of my FF installations (versions ranging between 53 and 56) to PaleMoon, where addons work as they should. So next time folks at Mozilla ponder why their market share dropped again, this is why - arrogant ignorance of legacy version users doesn't pay off.