Honestly, I just have to wonder what the Mozilla devs do. Don't they use extensions? Didn't they notice what was going on? Why does it increasingly feel like a more random Google Chrome-Lite paired with Apple's 'best intentions'?
This is a certificate that expired, not some insufficiently-tested change someone deployed. Mozilla devs had their extensions disabled at the same time as everyone else.
Well, most of the actual developers probably run Daily and have xpinstall.signatures.required = false, and are therefore not impacted quite as severely.