Just go on the page of any doujinshi, open the extension and download it.
Don't want to download them inside a ZIP file? You can choose your favorite format in the extension's option between zip, cbz and raw.
Go on any page containing doujinshi and download them all at once!
You can even use that to download the doujinshi in your favorites.
Want to download all the doujinshi with some tags?
Go to any page with doujinshi and download all of them, along with the next pages.