TL;DR Mozilla doesn’t sell data about you (in the way that most people think about “selling data”), and we don’t buy data about you. We changed our language because some jurisdictions define “sell” more broadly than most people would usually understand that word. Firefox has built-in privacy and security features, plus options that let you fine-tune your data settings.
https://youtu.be/4litc5DxoHQ
https://blog.mozilla.org/en/firefox/update-on-terms-of-use/
https://github.com/mozilla/bedrock/commit/d459addab846d8144b61939b7f4310eb80c5470e#diff-a24e74e4595fa85440a2f4e7e5dcfe68aba6e1e593aef05a2d35581a91423847R59
Removing “no we will never sell your data” from your Q/A page is not a good look