If you're having problems with extensions since midnight UTC, turning off signature checking works:
1. install ESR, developer, or nightly edition
2. open about:config
3. change xpinstall.signatures.required to "false"
you can now re enable all extensions


J'ai trouvé plus simple si on est en FF 66.0.3 ,ça a marché pour moi:

Another (probably better solution) is provided by u/FlickFreak:
Fix available for 66.0.3:

@thierryb but you should be well aware of what this extension will do

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