Together with the great State partitioning feature, Mozilla rolls out "Sponsored Top Sites" basically advertisements on your "Home" page.

https://support.mozilla.org/en-US/kb/sponsor-privacy

While I don't mind them creating alternative revenue streams, they should, especially with something traditionally very privacy unfriendly, do it transparently. Instead their "anonymized tech data" links to a github repo without documentation ¯\_(ツ)_/¯