That is terrifying.
Only in the "Get Add-ons" section, mind you. Everything else is local.
Actually it is. It suggests the organization behind the browser actively takes steps to embed tracking right in the browser.
a) I can block it from websites easily. Not so from Firefox about:... pages.
b) Firefox has a marketing angle that they are privacy protecting. But injecting external tracking code into the browser itself is the opposite.
Homebrew also has it included with a pretty good description why I think: https://github.com/Homebrew/brew/blob/master/docs/Analytics....
That should be a whole lot more terrifying.