no, they do sell your data, they just make an effort to anonymize it:
We still put a lot of work into making sure that the data that we share with our partners (which we need to do to make Firefox commercially viable) is stripped of any identifying information, or shared only in the aggregate, or is put through our privacy preserving technologies (like OHTTP).
they used to think this technically didn’t count as “selling your data”, but some privacy laws are better written than they thought.
Wasn’t this just a change in the wording? They added a similar text in another file.
Edit: https://arstechnica.com/tech-policy/2025/02/firefox-deletes-promise-to-never-sell-personal-data-asks-users-not-to-panic/
no, they do sell your data, they just make an effort to anonymize it:
they used to think this technically didn’t count as “selling your data”, but some privacy laws are better written than they thought.