Why do some of my recent downloads have the original date instead of download date?

I've just discovered that a lot of files I've downloaded in the last few months have the original file date instead of the download date. This has created total chaos and confusion with my organization as I have no idea when I did anything! I presume Firefox has changed something. But why? When? What files does it affect? How do I change it back? And why weren't we told about this huge change? After over 30 years downloading files from the web, it's become second nature that downloads always take the download date. A monumental change like this needs to be clearly signposted or it's going to create chaos with people's file systems and organization. '''Update: '''On reflection, I think this is a Windows 10 bug, rather than a Firefox issue, so perhaps this thread should be deleted? I looked at the properties of the files in question and discovered that all three dates DO match the download date. The problem seems to be that WINDOWS ITSELF is displaying EXIF data dates instead of modified date. I only recently started using Windows 10 and this would seem to be a Windows 10 bug.