(cont…)
Those cookies are shared across Amazon, and to about any website you go to where they have advertisement pop-up.
I doubt Google or Microsoft are sharing cookies with Amazon. Both are directly competing against Amazon, including the ad space where this data is quite lucrative and helps in competing.
Furthermore, the content of the cookie itself is probably meaningless to Amazon. Even if they grab a Google cookie, it isn’t going to reveal to them all the YouTube videos you’ve watched and Google searches you’ve made. Cookies, by nature, should be kept small, possibly with only an id used to identify the user, with the bulk of the processed data living on the server. Amazon doesn’t have access to that for Google or Microsoft.
What is more likely is that Amazon manages to use cookies as a third party on sites. For instance, if a site’s ads go through Amazon’s ad network, they may, as part of the API, grab Amazon-related cookies and log that you visited X site about Y. If this is a concern, or if you just want to know what cookies exist as third party on a site, modern browsers should allow you to block third party cookies and only whitelist those you want to. I know on Chrome, the option is found under:
Settings → Advanced → Privacy and Security → Content Settings → Cookies → Block Third Party Cookies (might be on by default, can’t remember)
After that, third party cookies will appear in the address bar on the right near the bookmark star. It works well enough that it even blocks some of Google’s cookies on its own sites.
Those will have Ads generated based upon the sites I visited or the tools I searched even on Amazon.
Just like Google doesn’t share data with Amazon, I’m reasonably certain Amazon doesn’t share its data with Google. That said, if you want to know what Google has found out about you through Search, YouTube, News, account settings, etc. (GSuite apps like GMail aren’t tracked for ad purposes anymore), you can go to:
myaccount(dot)google(dot)com → Review Your privacy settings → Make ads more relevant to you
There you can view info and even make the ads better. The page before that is also great for managing privacy settings and seeing how data is used.