How to get the original HEIC file out of iCloud Photos on the web?

I take photos on iPhone with HEIC image support. How can I get the original HEIC file from iCloud Photos on the web, when browsing on Windows? I'm using Firefox on Windows 10. When I download a single photo from https://www.icloud.com/#photos that is (presumably) HEIC because it has HDR and Live photo, I get a ZIP file containing a JPG and a MOV instead. (Yes, I really want the original HEIC, for testing software)