Unfortunately that isn't a Firefox software so Firefox user can help or diagnosis why that downloader isn't working. You need to contact the download developer for help on their software issue.

Thanks for the reply. How do I get in contact with the download developer?

Hi Anton, I assume you are using an add-on. When you visit the page on the Mozilla Add-ons site for that add-on, the Description or one of the boxes in the left column should have contact and support information. Or if you purchased a license, you probably know the company's website already.

OK, thanks a lot for getting back to me.

Anton