`firefox-send` is a script for Nautilus/Nemo/Caja (maybe it needs some adaptation for Caja) to send files directly from the file browser, using the contextual menu.

* Copy the `firefox-send` file to ~/.local/share/nautilus/scripts/firefox-send
* Modify the default options to your use case: host server, download number, retention time.
* Make the file executable (`chmod +x firefox-send`).
* Restart Nautilus/Nemo/Caja.