Hi Stephane, I think this warning is based on data from the Google SafeBrowsing project:

https://support.mozilla.org/fr/kb/comment-fonctionne-protection-contre-hame%C3%A7onnage-et-logiciels-malveillants#w_comment-fonctionnent-les-protections-contre-lhameconnage-et-les-logiciels-malveillants-dans-firefox

Perhaps there is a Debian forum where they can consider this and advise you on whether that is a safe download?

The English article is https://support.mozilla.org/en-US/kb/how-does-phishing-and-malware-protection-work#w_how-does-phishing-and-malware-protection-work-in-firefox

Is this really a warning from Firefox or a warning from security software on your computer since you are downloading a Linux ISO image on a Windows computer ?

Can you attach a screenshot ?

• https://support.mozilla.org/en-US/kb/how-do-i-create-screenshot-my-problem
• use a compressed image type like PNG or JPG to save the screenshot

This was how it looked on mine (Windows 10). There was nothing unusual until after the download was completed. At that point, the process seems to have paused because the .part file was not renamed to or merged with the real file name.

I checked the downloaded file and the SHA512SUM matches the listed checksum.

• https://cdimage.debian.org/debian-cd/current/amd64/iso-dvd/SHA512SUMS
• https://www.debian.org/CD/verify

a577aa8b7bd798dc20120c89432a2485d1cb10e3b2ebe987a91265ca028b5293ccd32f43bb1578ba3cd59390b8d77fa3c5ecfa8239974f2772a437085d8182f8 debian-10.5.0-amd64-DVD-1.iso