Important context!

They had to change this because newer laws like the CCPA classify some ways of transferring/processing data as a “sale”, even if no money is exchanged.

What? No. Do you really think their "sharing" with "partners" who are "providing sponsored suggestions" doesn't involve money being exchanged? 🤔

Here is an abridged version of that FAQ entry consisting only of substrings of it:

The reason we’ve stepped away from making blanket claims that “We never sell your data” is because [...] to make Firefox commercially viable [...] we collect and share some data with our partners, including our optional ads on New Tab and providing sponsored suggestions in the search bar

All of the other words in there implying that they had to stop promising not to sell user data because of some (implied to be unreasonable) "LEGAL definition" of "sale" is imo insulting to the reader.