Rated 4 out of 5 stars
Very good add-on, and agree with the suggestions from Terepin, missing two features:
- Open DM in background
- Close DM after download is completed.
I didn't check the code for those two specifically, but I think I made both to follow the preferences that exist for those things on the normal download manager, so actually both of those should already work if you switch the correct prefs, which you can find in normal Firefox download manager docs.