Oh my! Firefox disabled all add-ons because a certificate expired

Well, only those who do nothing do not make mistakes.

Here’s a quick workaround:

For now, there is at least one workaround, but it only applies if you’re using the Firefox Developer or Nightly build. If you look under “about:config” (if you don’t know what this is, you probably shouldn’t try it) and set the “xpinstall.signatures.required” value to False, then your extensions will start working again.