How do I stop Firefox from forcing https:// on local development server?

I am running a development environment on my Macintosh using AMPPS.

I have a folder with my project files. I have added this to my hosts file:

127.0.0.1   www.example.com

and I have set up the virtual domain accordingly.

When I attempt to connect to the site using Firefox:

http://www.example.com

it always redirects to:

https://www.example.com

and then complains about it.

The folder has nothing else in it but a dummy index.html file.

When I test the site in lynx or in Safari or Chrome, I get to my sample site. When I test in Firefox, that’s when I get the problem.

Firefox is my main browser, so it is possible that I have a caching problem, but I cannot see any method of clearing the cache that I haven’t tried already: trying to forget the page or clearing the cache.

I have tried all the suggestions mentioned here and elsewhere, but I am obviously missing something.

How do I stop Firefox from doing this?