For me, the "fix" didn't work. Possibly because I used the OverNight build. FF removed all the extensions EXCEPT for the ones that I had disabled.
Now I'm trying to recall what extensions I had and re-install them one by one.
After this, I think I'm going to have a look at Vivaldi. What does it say about the competence of an organization if they can neglect renewing a certificate -- a certificate that they had forced developers to use in the first place?