Thanks for the rating, glad you like it.

Your feature requests are kinda asking for a lot though. Detecting duplicates is way out of scope for a simple addon, trying to find linked bigger versions of an image is a logistical nightmare while a user can do it himself easily, and downloading all in an area is a very tricky thing to do. Determining the "pattern" will often not have the result users want either and will be heavily affected by every individual website's structure.

I get the feeling one of your underlying problems can be solved another way: I use my other addon Copy Selected Links to get the full-res links of images in a thumbnail gallery, and throw them into jdownloader or similar programs to get all the full-size pics. Maybe that solves one of your problems?

This might also interest you: https://gitlab.com/Marnes/doubleclick-image-downloader/issues/35

Mozilla has nerfed the addon api and addons are not able to do as much anymore as in the past.

As for the custom download folder, that's an anti-feature. The browser has a downloads folder so all browser downloads will and should go to that folder. My addon can download images to a subfolder of it, but that feature is not available in firefox yet because the api is not complete yet. It will be possible to use subfolders again at some point in the future, but the browser downloads folder will always be the starting point - it's a matter of technical complexity, reliability, cross-platform operation, and sane design.

What happened? Firefox became a completely different browser under the hood, that's what happened. And a lot of power was taken from addons, a compromise that had to be made to ensure quality in future addons. Don't like it? Switch to chrome, that's what I did.

Edit: yeah, you can roll back to a previous version and switch off auto updates on a per-addon basis. I wouldn't wait too long to update though because starting with firefox 57 the older versions will simply not work anymore.