[#23023] Picker for Firefox: Installation error 203

I am trying to install the Citavi Picker for Firefox, but I get the error "Unexpected installation error -203."

This error is usually caused by corrupted settings files (see Unexpected installation error -203)

To correct this error:
  1. Exit Firefox
  2. Open your profile folder
  3. Delete the following files:
    • extensions.ini
    • extensions.cache
    • extensions.rdf
  4. Restart Firefox.
  5. Reinstall the Picker for Firefox.
Install Citavi again by double-clicking the Setup file. Alternatively, install the Picker for Firefox by opening the Windows Control Panel and then clicking Programs and Features. Select Citavi [version number] and then click Change. Click Next, then select Modify and click Next again. Click the red "X" next to Picker for Firefox and then select This feature, and all subfeatures, will be installed on local hard drive: