I wonder if you will get excoriated for this opinion, since I had to respond to people in my last post with an update because people were adamant that Firefox was open source. 😼

https://blog.mozilla.org/en/firefox/firefox-labs-fx138/

I wrote up what happened (more stuff on my blog).

TL;DR they use aggregated data for ads and they felt like they needed to have an explicit opt-in.