Thank you for review.

In the previous version, you will need to drag and drop twice. So I updated.
I also want to keep the default save folder, but unfortunately I couldn't do it because of the API( ；∀；)
↓ See the filename section.
https://developer.mozilla.org/ja/docs/Mozilla/Add-ons/WebExtensions/API/downloads/download

2020/04/26
The same download as 4.2 can now be done by holding down the control key and dropping it.