After an update Firefox won´t let me add extensions.

Hi! I´m using Jdownloader2. After an update of Firefox the captcha-extension of JDownloader didn´t work anymore. I reinstalled Firefox, but adding the extension is still prevented. Following quote appears: "Firefox hat die Website daran gehindert, Sie zu fragen, ob Software installiert werden soll" It should be in yellow (but it isn´t), like following site describes: [http://example.com https://support.mozilla.org/de/kb/Add-ons-koennen-nicht-installiert-werden#w_firefox-hat-die-website-daran-gehindert-sie-zu-fragen-ob-software-installiert-werden-soll] Furthermore there should be a button to authorize the installation. Instead there is only the button "OK". I followed the help-site mentioned above to the letter, to no avail. By the way, I´m using Nightly now, but JDownloader2 automatically wants access to Firefox. Would you please tell me, how to add the mentioned extension. Without it I couldn´t download most files! Please answer to following email: [redacted email from community support forum] Best regards, Stefan P. aka perechon