After installing Downloadwith
Click on Tools | Options | Extensions
In "The following extensions are installed" box -
Click to select DownloadWith v0.0.7 and then click on "Options..." (bottom right corner)
Click on "Create New Application"
The "Download Sample configuration" radio button should be selected by default. If not, click to select it.
In the Download sample configuration box below there is a list of all kinds of download programs.
Click to select the download program you want to configure with DownloadWith (presumably one that you have installed on your computer).....DAP in your case
Click OK to close "Create new application settings" dialog.
Click OK to close all other dialogs.
Restart Mozilla Firefox.
Now to use DownloadWith ~
Right click on the download link, scroll down to hover over DownloadWith and then in the flyout menu you should see your download program listed.
Click on it to start the download.