You may need to reload a page the first time after installing this addon. Double-clicking a regular image just works by itself (note that not everything that looks like a regular image on your screen will be detected as such, but the vast majority will be). The hover button also does not just show in the middle of the page in normal circumstances. but on an image. If this is your experience, you're testing it on just 1 website, and one that happens to do odd things this addon can't support with images. Please try it on other sites too before judging, or open a ticket on gitlab (or email me) and at least link me to the page so I can have a look.

Assuming the translation by google is correct: I won't build site-specific support into this tool. It's meant to be a generic image downloader that works well on sites with conventional HTML structures that expose images in an accessible way. Instagram is one of those sites with overly complicated, image-hiding webpage structures. I find a 2-star rating just for not working well on instagram a bit superficial since there's so much more to this addon and it works fine on most websites, but ok.

I'm not sure if the correlation is 100%, but you're right in that it will definitely work if "save image as" is available, and when it isn't, it'll be uncertain. I think there used to be code that looked for images more agressively so it would work more often, but then it started making virtually everything downloadable (page backgrounds, buttons, etc), which was horribly annoying too. 10/10 very fair review. :)

This addons works just fine and has the most important things it needs (and then some - I already find it too bloated compared to my original vision for it). I don't think it's fair of you to rate the addon itself lowly just because I don't implement all the non-essential extra fluff people open up request tickets on gitlab for. Ratings are supposed to indicate/be based on the quality of the addon as it is right now, not be used as a knife to put pressure on devs to add extra features you want. If it works fine for its intended use and has some extra bells and whistles, you can't justify 1 star.

Unfortunately not all websites are the same, and some use all kinds of layout tricks that prevent addons like this from realistically working, or even specifically protect their images from copying tools. I feel like you're trying to paint this as a shortcoming or flaw, but that's a little unfair. Webdevs will always find ways to hinder tools like this, on.purpose or coincidentally. There is no addon that works perfectly for all.

Update: yes, of course any visible image is by definition available to download, the problem is with websites doing all kinds of weird-ass shit to satisfy their sometimes arbitrary layout decisions and completely violating web standards in the process, or just using complicated css nonsense that can completely throw tools like this off-track. My addon is able to work through most of those things, but you can't expect 1 generic little piece of code to be able to perfectly circumvent everything a human dev can come up with that makes its life harder. Write an algorithm yourself and submit it in a PR, Mr. Perfect, or be satisfied that it works 99% of the time.

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.