Thank you for your feedback and I'm sorry that you're experiencing some issues. You can report the issue on https://github.com/baptistecdr/aria2-extensions/issues with the links that you try to download.
When you download a file, Firefox will prompt you this dialog : https://i.snipboard.io/evwo9r.jpg, choose "Save file (Enregistrer le fichier)" and then OK. Your download should be captured.
