firefox 57 and still do his work.
I just dislike the balck background on empity list, but it is forgivable. MAybe putting some option for like icon to preview for image/video, background color(s), height/widht, ecc?

Works as it is intended to but I'm not sure if I'm missing something, is there an option to have the pop up open automatically when a download starts?

With that said, it could use some improvement. What I would like to see changed, if it were up to me, is I'd like the popup to be resizable, and I would like to see the look of both the popup as well as the icon integrate more into the look and feel of the Firefox browser, whether themed or not. I would then surely give it a 5-star review. :)