D4X
 

I've successively installed D4X. It works fine. I want to make it my default downloader. I'm using mozilla firefox in Slackware.

Have you checked here?
https://addons.mozilla.org/en-US/fir...e/type:1/cat:5
Googling would be a good skill to learn.
jdk

Yep, it's the flashgot extension that you want.