Safari's tracking policy is in large part intended to protect users against the Facebook ecosystem (even though, yes, it is not specific to Facebook or any other domain and just establishes policies for technical behavior): https://www.theverge.com/2018/6/4/17427000/wwdc-apple-safari...

> Cross-site tracking is tracking across multiple first party websites; tracking between websites and apps; or the retention, use, or sharing of data from that activity with parties other than the first party on which it was collected.

I think that having Facebook share tracking information with Repixel and in turn with Repixel's customers counts as "sharing of data from that activity with parties other than the first party on which it was collected," no?