DensityDesign does not accept a csv file (windows)

[miriam-s]

When I try to upload a csv-file with image-URLS, the DensityDesign tool (https://densitydesign.github.io/dd-image-tagging/) says "This is not a csv".
Computer: Acer swift, Windows 10
Browser: Firefox, Version 77.0.1. (64-bit)
It also does not work for google chrome or another windows computer. Are there solutions for windows computers?

I am testing it at the "corona testing on Twitter" workshop: https://warwick.ac.uk/fac/cross_fac/cim/news/covid-19-testing-on-twitter/