It's literally in the text. The sponsored content (ads) are picked based on the data they have from you. This is segmented advertisement: they don't sell your home address to advertiser, they sell them which cohorts you belong to. Advertisers buy Mozilla ads for "men, 25-35, great London area, interested in winter sports" and Mozilla use the data on your browser to determine you fill those requirements and show you that ad.
And this is, exactly, how both Meta and Google make money from their users.