Information
This feature indicates whether the user is warned before opening an external application for pre-configured protocols were its behavior is undefined.
Enabling a warning to appear before passing data to an external application mitigates the risk that sensitive information will be made vulnerable to outside threats.
Solution
Perform the following procedure:
* Open the mozilla.cfg file in the installation directory with a text editor
* Add the following lines to mozilla.cfg:
lockPref("network.protocol-handler.warn-external-default", true);