Firefox

I recently downloaded Firefox Nightly and noticed some new settings that were enabled by default:

• Suggestions from Firefox Nightly
  Get suggestions from the web related to your search
• Suggestions from sponsors
  Support Firefox Nightly with occasional sponsored suggestions

Learn more about Firefox Suggest

The link in the UI doesn't mention sponsorships anywhere. But this page does:

Who are Mozilla’s partners for sponsored suggestions?

We partner with organizations to serve up some of these suggestion types... For sponsored results, we primarily work with adMarketplace, while also providing non-sponsored results from Wikipedia.

This page links to the adMarketplace Privacy Policy which makes it pretty clear this company is okay with collecting your IP address and passing it to further unnamed entities.

Elsewhere, they say Firefox sends them "the number of times Firefox suggests or displays specific content and your clicks on that content, as well as basic data about your interactions with Firefox Suggest", and then will share interaction information "in an aggregate manner with our partners".

Update: Switched the link from the Desktop to the Mobile version. Added more quotes from FF, and bolded info about their one named AdTech partner.