Unfortunately it is not possible to implement what is described here. Indeed it would require Firefox to have a write-access permission on the Windows Registry, which is not safe. (respectively on Linux, a write-permission to directory “~/.mozilla/native-messaging-hosts”). This add-on and the DZA! application communicate through "Native Messaging", which is the compliant method provided by Firefox and Chrome.

https://developer.mozilla.org/en-US/docs/Mozilla/Add-ons/WebExtensions/Native_messaging

https://developer.chrome.com/apps/nativeMessaging

=> the solution is to run “install.bat” (conversely “uninstall.bat”) provided in the portable's ZIP, in order to let Firefox know the right path to the application.

PS: or edit manually the app's path from the Windows Registry (resp. Linux ~/.mozilla directory).