In Firefox, www is automatically substituted for all sites - how to fix this?

Question

Mozilla Firefox

The crux of the problem is in the title. instead of 127.0.0.1:8000 I stubbornly have www.127.0.0.1:8000.
The problem does not occur on all sites and only in FF, that is, in the same Chrome everything is in order. What settings in FF are responsible for such a substitution?

Answer 1

Try disabling all plugins

Answer 2

setting
browser.fixup.alternate.enabled may help

Answer 3

http://127.0.0.1:8000and everything will work