That was actually a server-side bug 8 months ago which they not only fixed within 3 days of the issue being reported but followed it up with a hard block against more than 2 displaying at once to make extra sure this didn’t happen again.
If this is what you’re currently seeing then please report it to them. If instead this is an old screenshot then I’ll just agree that Mozilla has certainly suffered many avoidable self-inflicted wounds but this isn’t one of them.
Former employee here. Firefox has been adding sponsored content to the new tab page since Firefox 60 in 2018. Their support article gives a good amount of detail on how it works, but perhaps more importantly for you, how to disable it.