Firefox shows a popup and sends it to the site detectportal.firefox.com/success.txt what is it?

Question

Browsers

Recently, this line has begun to appear.

If you click on the button, it sends it to the address detectportal.firefox.com/success.txt, which redirects to the localhost. What it is? How to disable this popup (more precisely, how to disable it, I kind of googled it, but I'm trying to understand what it is all about ???)?

Answer 1

https://webmasters.stackexchange.com/questions/104...
https://searchmobilecomputing.techtarget.com/defin...
How to disconnect - you need to ask the person who provides you with a connection