The Firefox Browser is a privacy nightmare on desktop and mobile
privateinternetaccess.com
privateinternetaccess.com
Meanwhile, the article is coming from a company that's selling privacy on a for-profit basis, towards a non-profit focused on attempting the best privacy possible. Most of their products are in the same space as Mozilla.
They are very openly using the least amount of data possible in order to know how people use the browser so that they know what to focus on to make things better, or what to fix that isn't working. They don't care who you are, all they want to know is how you are using their product so they can keep making it better.
You can check everything that is being sent to mozilla at:
about:telemetry
and as you can see there is nothing that identifies you. And even if i'm missing something, you can always disable telemetry and be sure that (unlike others) firefox will respect your config and won't be sending any data
However, I think this makes it clear that privacy is not automatic by default.