Firefox 43 Disables Older Picker Versions

The current version of Firefox blocks the installation of unverified add-ons. Older versions of the Citavi Picker are affected by this change.
If you see the message Citavi Picker could not be verified for use in Firefox, in the Firefox Add-ons manager, install the update to Citavi 5.2. In Citavi 5.2 the Citavi Picker for Firefox is verified:
If you still are working with Citavi 2, 3, or 4, install the upgrade to Citavi 5 (see our manual for more information). If you are using a site license, the upgrade is free. If you purchased Citavi 3 or Citavi 4, you can purchase Citavi with a discount. Click here to request your coupon.
Updates do not affect your Citavi projects or documents created with the Citavi Word Add-In. Afterwards you can continue working as you normally would.