Attention! VERSIONS AFTER 2.1.4 are not original plugin!

VERSIONS UP TO 2.1.4: Thanks a lot! This add-on saves a lot of time. Musthave!)
"It would be great to be able download certain songs separately, not a whole playlist" - my mistake) just click on the song and add-on will offer to download only this selected track.
Downloader doesn't ask the folder to save, it takes the last path Firefox used to save.