megalomaniacs4u has found a more elegant solution that you probably want to try first. It achieves the same goals (importing a good certificate, re-verifying your add-ons) in fewer, easier steps.
This is an interim fix for Armagadd-on 2.0 on Firefox 61, 56, and potentially other old versions. As of this writing, Mozilla's official hotfix XPI doesn't work on these versions, so manual workarounds are needed.
This process successfully reactivated my extensions on Firefox 61 and Firefox 56 under Windows. It also worked on an old copy of Firefox 48 for Mac OS X. I can't promise that your add-ons won't be disabled again in the future, but this might get them working for now.
There are two objectives: one, get a working Mozilla signing certificate imported into Firefox; and two, tell Firefox to re-verify your extensions. You must complete all of the steps below. Use this g...