I think that's just a cover-all and they also have a privacy policy [1] which is explicit about how they use it and how they don't, for example:
"the data stays on your device and is not sent to Mozilla’s servers unless it says otherwise in this Notice."
... "When you perform a search in Firefox, your search query, device data and location data will be processed by your default search engine"
... "Mozilla derives the high level category [...] from keywords in that query [...] privacy preserving technologies such that Mozilla only learns that someone, somewhere, performed a search relating to a particular category, without knowing who."
... Review Checked, AI Chatbots, advertising on new tab page, etc.
So yea Firefox does so much they pretty much have to use your data, but it's not a blank cheque to do what they want.
"the data stays on your device and is not sent to Mozilla’s servers unless it says otherwise in this Notice."
... "When you perform a search in Firefox, your search query, device data and location data will be processed by your default search engine"
... "Mozilla derives the high level category [...] from keywords in that query [...] privacy preserving technologies such that Mozilla only learns that someone, somewhere, performed a search relating to a particular category, without knowing who."
... Review Checked, AI Chatbots, advertising on new tab page, etc.
So yea Firefox does so much they pretty much have to use your data, but it's not a blank cheque to do what they want.
[1] https://www.mozilla.org/en-US/privacy/firefox/
Not so say I like some of those things - advertising and categorizing searches. But still, it's finite and explicit.