That FAQ is full of misinformation and poor writing. The second point ("What is a cookie?") includes:
"To personalize your web browsing experience and to make the Internet work operationally,"
Make it work 'operationally' as opposed to ...? Anyway, as we all know, cookies aren't a requirement for the Web to work, let alone the Internet.
"websites you visit"
Correction: some websites ...
"place (or allow their approved partners to place)"
No mention that 'approved partner' is utterly meaningless
"a small harmless file, called a "cookie", in your browser."
Congratulations - apart from the slightly strange use of the word 'in', this is correct
"Cookies contain numbers and letters that identify your web browser, but not you personally."
Just utterly wrong
It does not contain your name, address phone, email or other information that can personally identify you."
Well, 'it' could, of course, so another meaningless statement
"Companies use cookies to learn more about user interests through users’ web browsing activities and to remember the preferences you set on their sites, such as the language you like to read, the last items you purchased, and the resolution at which you likes (sic) to watch videos."
"you likes" - seriously? Is this organisation just a kid in his bedroom?
"For example, a cookie can tell a website that you’re a repeat visitor, and then can let the site fill in your username for you."
As, of course, can your browser.
The fact that these people obviously have very little understanding of the issues they're talking about just convinces me we need responsible organisations like Mozilla to help prevent them from exposing us to privacy and security risks.