Honestly I don’t think I’m technically adept enough to check this myself. I was following firefox privacy guides, and the (much more competent) people writing them were puzzled about those two.
Of course it’s not necessarily malicious, but it has became hard to be trusting.

In the end I kind of just gave up on privacy, I take mitigation measures as a symbolic gesture, but still assume someone’s watching over my shoulder whatever I do online. Not a good feeling to be honest.

How would I check exactly what data firefox is sending home?

firefox.settings.services.mozilla.com
content-signature-2.cdn.mozilla.net

There are unexpected connections to these two domains that cannot be disabled using firefox options.

Easily? How?
AFAIK no matter what you do, firefox still calls home sometimes.

From what I can tell, the idea is to make you feel like, with a little bit of effort, the privacy thing would be achievable,
but when you actually try, it’s a whole different ordeal.

All advertising is harmful, a complete ad ban would be wonderful, very hard to enforce thought.