Firefox removed FTP support some months ago. Ironically when I copy paste that link it now prompts me to open it in Chromium.
That might sound crazy (FTP is an ancient protocol), but I spend a lot of time scouring FTP servers for old technical reports. Mozilla can't just wish FTP away.
Maybe it was removed for the Windows build? If so, what a bad decision, maybe for security reasons?
I normally use FF Nightly which explains the difference.