You could start by reading the article, even only the first paragraph:

> Firefox asks for your permission before connecting to a website that doesn’t support secure connections.

As other posters mention, you can disable this when you need to, but also browsers generally treat localhost and/or 127.0.0.1 as secure origins in themselves anyway, so I suspect that won't be necessary. See https://developer.mozilla.org/en-US/docs/Web/Security/Secure...:

> Locally-delivered resources such as those with http://127.0.0.1 URLs, http://localhost and http://*.localhost URLs (e.g. http://dev.whatever.localhost/), and file:// URLs are also considered to have been delivered securely.

As described in the article HTTPS-Only mode is opt in, you can also disable it at will, you can add exceptions on a site-by-site basis, and even when it's on you are prompted on whether or not you wish to proceed to non-HTTPS sites.

My guess is that either there's a built-in rule for that, or you can just click the "Continue to HTTP Site" button like in the screenshot.

It's explained in the post:

> For the small number of websites that don’t yet support HTTPS, Firefox will display an error message that explains the security risk and asks you whether or not you want to connect to the website using HTTP. Here’s what the error message looks like: ..

"Firefox asks for your permission before connecting to a website that doesn’t support secure connections."

That suggests it will ask you for permission, presumably with a "always remember this choice" option.

It would help greatly if this kind of things (that and security exceptions would not apply to any host in the RFC1918 address space. Would make life easier for IT dept around the world.

From the article: Firefox asks for your permission before connecting to a website that doesn’t support secure connections.

It will probably be a hardcoded exception, just like for enabling microphone/webcam access and other features today.

Just tried it after enabling the feature - No message, accessing localhost works just fine over http.