Why do default Amazon searches append a seemingly non-Mozilla affiliate tag to the url?

Searches using the provided Amazon search feature found in settings will always have "tag=admarketus-20" in the url. Example: https://www.amazon.com/s?tag=admarketus-20&ref=pd_sl_ [bunch of letters and numbers] &mfadid=adm&k= [search query] Now, if this were an affiliate tag for Mozilla specifically, I would understand, but googling the "admarketus-20" tag turns up posts showing that users on various other browsers (Vivaldi, Opera, Chrome) also reporting seeing this tag popping up in their searches too. I wondered if this was due to malware, but I did a fresh Firefox installation on a newly installed Win10 machine and it happens there too. Who/what is this tag for?