The download sound doesn't play when download finishes. All music, game audios, and other system sounds play normally, only Download Manager (S3) will not play. Using the default sound (Checkmark), and the option is checked. The add-on also does not delete download files, then the folder containing them is opened, even though that option is checked. As such, this add-on is no better than the default Firefox download, and so there is no good reason to use it.