Firefox extensions disabled for many users due to certificate issue
EDIT: Fix & more info posted on Mozilla blog: https://blog.mozilla.org/addons/2019/05 ... n-firefox/
Huge bug affecting many users right now: https://bugzilla.mozilla.org/show_bug.cgi?id=1548973
Looks like a signing certificate expired, causing many extensions in Firefox to be disabled, without the ability to re-install as it gives an error.
The only solution at the moment is to use dev, nightly, or ESR builds, point it to your old profile via -profilemanger & disable xpinstall.signatures.required in about:config, from what I understand.