Downloading to a folder outside the browser's default download dir is not possible (even if I wanted to, it cannot be done) and an anti-feature anyway for technical reasons (hence why they made it impossible).

Sorry about the subfolder and rename feature being broken at the moment, but that's due to firefox's incomplete API. It works in chrome.

If I remember correctly, nstagram is one of a few hosts that have a very strange internal layout on their webpages that makes it impossible or very difficult for an addon to download their images. Twitter and a few others are also guilty of it. I can give them another close look to see if I can fix it but there are no promises.