The root certificate is also part of the mozilla.rsa. Addons have it included, it can be extracted and then imported into the browser Certificates > Authorities

The root certificate is also part of the mozilla.rsa. Addons have it included, it can be extracted and then imported into the browser Certificates > Authorities and it will be used to validate addons, including those which are not updated. A sample procedure doing exactly this, and a fix for Firefox <= 56.0.2 can be found here: https://www.velvetbug.com/benb/icfix/ https://www.velvetbug.com/benb/icfix/ The same procedure can be used on newer versions, but the syntax is a bit different (import cert, go to about:addons, open console): Components.utils.import("resource://gre/modules/addons/XPIDatabase.jsm"); XPIDatabase.verifySignatures(); This only makes sense if you really need to fix it while the browser is running, otherwise you can simply restart it after the new certificate is imported.