Facebook, Amazon and Firefox

[Sauron]

So I have a question about how Firefox works.

I've been seeing my Amazon browsing showing up as advertising in my Facebook feed. It's pretty annoying and a little creepy. I have not given Amazon permission to do this, or granted the Amazon app any rights in Facebook.

I've seen the same thing with Expedia showing up in my Facebook feed. Trips I am planning in Expedia start showing me destination-related restaurants or other attractions in Facebook. The only common element that I can find is that I tend to always use Firefox, and sometimes they might be in adjoining browser tabs.

Could this be cross-pollination be happening in the browser instead? Does an application in one Firefox tab have access to any other tabs, and whatever websites are there?

Would in private browsing block this?

Thanks for any info.