Huh, that's just security theater. The phisher could set up a website that does require authentication, thereby avoiding the warning.
The sensible thing to do would be to display the warning if the username contains unescaped dots. (I.e., http://cnn.com:article123456@fakenews.example.com/ would provoke warnings, but http://cnn%2Ecom:article123456@fakenews.example.com/ would not.)
http://news.ycombinator.com@1572395042 Chrome takes me to 93.184.216.34 no warning
Then I tried http://security.wellsfargo.com@customerLoginv=ar3351RandomDa...
Which stretches way past my laptops viewable URL bar... and it takes me right to badsite.null (or a valid site like example.com). If you need HTTPs you can redirect on badsite.null's web server. Very wild.
In the name of security the change way too many moving parts lately to push their hidden agenda.
Using HTTP in local LAN is fine. Using HTTP for non login-pages is fine. Using "basic authentification" (user:pwd@IP) is fine for certain use cases. Stop breaking things.
I am not using a Firefox anymore, they went insane lately, they don't bother about their community anymore. I am worried about Chrome too, TLS only for HTTP/2 is the wrong signal. So many times I couldn't open a HTTPS sites because the browser thinks the cert is broken - it was just a trivial page were I just want to read some text (not input anything) - just some me the page - something that wouldn't be a problem with HTTP.
If Firefox, Chrome or whoever want to destroy access to 1994-2017 websites, go to hell. Name your forked off thing TheMicrosoftNetwork (or what not) and see it tank rather quickly.