On most computers I use the DownThemAll addon for Firefox as my download manager. But, on an old computer I recently found that Firefox was too slow when addons were used. I found that the uGet download manager program acts as a good alternative to using a browser addon. Installing uGet is easy:
$ sudo apt install uget
A few features of uGet to note:
It can be minimized to the system tray where it will monitor the clipboard for URL ending in certain file extensions.
Downloads can be queued, paused and resumed. This can be done even between program or computer restarts.
Download will be performed using multiple connections in parallel automatically when needed.
Tried with: uGet 1.10.4 and Ubuntu 15.10