Go to the Mozilla Add-ons Web Page {web Link} (There’s a lot of good stuff here) and search for a download manager.

This download manager works separately from the browser. The browser tells it what to download, and off it goes.

http://www.freedownloadmanager.org It is a powerful modern download accelerator and organizer for Windows and Mac.

It is possible that (anti-virus) security software is causing the problem. Try to disable security software temporarily to see if that makes a difference.

@cor-el ,

Thanks for the reply.

I tried disabling anti-virus and reinstalled firefox. This is not sorted out. Any further help ?

Changed the permission of the Downloads folder to fix the issue.

That was very good work. Well Done.