how to block coection to a domain in firefox

i need to utterly block a domain from even being coected to. obviously, addons wont work, since those only check the URL of the site the browser is navigating to, not domains the browser is coecting to. i need firefox, but preferably every browser to refuse to even make coection with the domain wherever and whenever they are being coected to, for example in an iframe, or loading an image from them on a site with a different URL.

changing the hosts file at C:windowssystem32driversetc did NOTHING at all. writing this as a test: 127.0.0.1 google.com 127.0.0.1 www.google.com anywhere in the file did nothing, and i could still coect to google.

as a reference, i would need something like when a website has an invalid certificate. when that happens, firefox refuses to even coect to the domains. would it be possible to assign an invalid certificate to specific domains, so that they get blocked? also, every hosts file changing addon i tried for firefox changes the windows hosts file, and it obviously doesnt work. is it possible to change the actual settings firefox uses instead?

also, i am using windows xp, but that shouldnt mean its impossible.