How do Facebook ads on my account reveal recent online shopping?

[YahooDeana]

Twice I have seen the exact item I found online appear the very next day on our facebook account - as one of those ads on the right.
How is Facebook tracking this info from my computer?

[Nick]

Facebook isn't doing it, the advertiser is.

You are a victim of "targeted advertising." To opt out, there's a small Ad Choices logo in the ad. Click on it and opt out of targeted advertising. You'll still see ads, but they won't be targeted. They do this by the search engines leaving a cookie about what you've been searching for lately.