Firefox on Twitter:
So sorry for the issue we’re having with add-ons right now!
We’re working hard to fix it and will keep you updated.
If you do not want to do without your installed add-ons, you can fix the problem with a fix: In the browser configuration (about: config) set the value xpinstall.signatures.required to false (then restart the browser). Thus, the add-on
ons ons - however, under about: addons they are still marked with a warning that they could not be verified for use. Attention: Turning off this feature is a security risk! You should definitely set it back to true later.
I have another Firefox problem on one of my fresh installs, there's only english language and in preferences there's no languages listed at all, and when you try to add - list is empty (it's all regardless if you have i18n packages installed or not).