Rated 5 out of 5 stars
Check the options: set the directory, file name format, and at what score the image will be automatically downloadedThe save dialog is usually disabled if you have set the directory and file name format as there's no need to type anything.
Just rate it and get the image. You can also force a download by pressing the purple button in status bar.
If downloading is started, a number indicating how many images are being downloaded will appear in the status bar.
It also keeps records of download history in ankpixiv.sqlite inside your firefox profile, which helps you to avoid duplicates.