By disabling JavaScript, as I do, that takes care of all of this. I enable it on occasion when I want to see a spoiler or pay a bill on-line. (This takes 4 mouse clicks. I wish I could set up a one-click button on my toolbar to toggle JS enabled/disabled.) This also breaks all the formatting tools and icons in the Compose Message box, but I’ve learned to hand-type the ones I use most, and keep a cheat-sheet handy of the rest. How retro is that :dubious: Being an old-school Command Line Interface junkie and troff user, that kind of stuph still comes natural to me. (We old 1980’s era Unix Sys Admins don’t need no steenkin mouses!)
Manually editing hosts like that sounds like more trouble than it’s worth. But I have a little in-house intranet of old machines that I’ve collected and various transient virtual machines that I play with, some of which do some kinds of server functions, but none of which do in-house DNS serving. So I have to add them all to hosts on all my machines! 
Here’s a thought! Write a Firefox add-on with just one or two clicks it will take the URL and IP of any page component I click on and edit that into hosts file for me!
Uh, maybe I’ll just look into script blockers. I like the idea of being able to build a site-specific list for what to block, just like Firefox does with cookies and images.
ETA: When I go to 127.0.0.1, it actually shows a stubby little “Hello World” web page!