I looked at the source code and indeed they put referrer IDs to the amazon links. It's even a dedicated ID for each link, to see the number of purchases for each link. So mozilla is taking part in the tracking.
They look like:
- fsclp_pl_dp_12
- fsclp_pl_dp_11
with each link having a distinct number, counting down to 1.
It doesn't look like a typical referrer ID, so it is probably something that Amazon generates, although I don't know under what condition.