Drag and drop with download

Hi all!

I need to figure out possibilities to do drag and drop with download.
I need to drag a link from a web page to mac desktop(or anywhere else) and
have that link downloaded when drag is finished. Also I need to control this
operation from JavaScript (to sypply a file name and a url to download
from).
Can I do this without modifications to the mozilla's source code?
I've already done some research on Windows - and figured out that windows
doesn't even support this kind of functionallity (at least by normal means),
now I have to figure out if it can be done on MacOS.

Thank you!
Yuri Kovalchuk,
Vested Development Inc, Saratov, Russia.