Firefox redirects to https

I had the same problem but the answer was that I used a .dev extension to access my local websites !

I cleared all historic data in FF and nothing changed.

Searching for another solution, I found this page https://ma.ttias.be/chrome-force-dev-domains-https-via-preloaded-hsts/

With .dev being an official gTLD, we're most likely better of changing our preferred local development suffix from .dev to something else. If you're looking for a quick "search and replace" alternative for existing setups, consider the .test gTLD, which is a reserved name by IETF for testing (or development) purposes.

I changed my local website extensions from .dev to .test and all work perfectly !

The solution that worked for me:

1. Go to about:config
2. Look for network.stricttransportsecurity.preloadlist and set it to false
3. Enjoy

If the above STILL DOES NOT WORK, try setting browser.fixup.fallback-to-https to false from about:config

Using Firefox 100 or above you may also need:

• dom.security.https_first to false
• dom.security.https_first_pbm to false (this one is for anonymous windows)

"Sites preferences" are the culprit. Wasted 45min of my life finding how to fix it despite all the kb/support.mozilla tricks which does not solve your issue nor did mine. I don't know what triggers this issue, but several of my websites started to go pear-shaped in a few weeks only affecting me and only firefox.

That's the solution you are all looking for:

1. Go to Preferences
2. Privacy
3. Click 'Clear your history' (nothing will happen yet, click safely)
4. Once the pop-up appears, click Details.
5. Untick everything except 'Sites Preferences'
6. Select 'Everything' in the select box at the top
7. Click Ok
8. Try now

PS: What I did try that did not worked for me are:

• urlbar.autofill false
• Forget Website trick
• Safe mode
• We all know it is not an HSTS issue when a website you own and you accessed before never got https support but now FF wants you to use https... It is just a firefox bug IMO.