I find myself downloading many PDFs for university twice or more because I can't keep track of which I already have downloaded and which not. So I end up having several versions of the same file in my Downloads folder, with (1), (2), etc. suffixes. I would like FF to check prior to a Download if I already downloaded exactly that file from that URL and if it still exists in my Downloads folder. If that's the case it shouldn't download the file again, but notify me somehow that I already have that file (maybe with an option to download again anyway, some web APIs are weird). I hope this is the right place to ask, I wasn't sure.