Firefox 93 now blocks downloads of HTTP files, from a HTTPS page. When you are on a page loaded over HTTPS and you click on a link to a file that will be downloaded over HTTP, the download is blocked and Firefox leaves the warning:
File not downloaded: Potential security risk.
The file uses an insecure connection. It may be corrupted or tampered with during the download process.
You can search for an alternate download source or try again later.
How do I disable the blocking and return Firefox's behavior to download such files as it used to, before Firefox 93?
(I do understand the implications well enough to make an informed decision about whether this is a good idea or not.)