"Your privacy comes first As the internet grows and changes, Firefox continues to focus on your right to privacy — we call it the Personal Data Promise: Take less. Keep it safe. No secrets. Your data, your web activity, your life online is protected with Firefox."

"At Mozilla, we believe that privacy is fundamental to a healthy internet."

While this is all good they have a lot of telemetry going on in the background.

"Interaction data: Firefox sends data about your interactions with Firefox to us (such as number of open tabs and windows; number of webpages visited; number and type of installed Firefox Add-ons; and session length) and Firefox features offered by Mozilla or our partners (such as interaction with Firefox search features and search partner referrals)."

Please see the rest here.

https://www.mozilla.org/en-US/privacy/firefox/

How can we really call this a private browser or even privacy-friendly browser while they are constantly hogging user data.