Seems to give an error when using it with Pixiv manga?
This is the url it sends you to: http://danbooru.donmai.us/uploads/new?url=http%3A%2F%2Fi2.pixiv.net%2Fimg10%2Fimg%2Fchouette%2F33705540_big_p1.jpg
EDIT: It also gives the same error with the "new-classic" bookmarklet, so it might be a problem with the upload screen...