This add-on is being promoted by Mozilla as a replacement for DownThemAll, but, in its current form, it is not. While it does have some useful features, it doesn't allow for making a partial selection from linked files or from embedded files. Bulk media downloader simply gives you all linked files in the form of a zipped archive. In its current form the add-on is slow and cumbersome (because it downloads things you don't want and because it might not download things you want).