In order to give its billions of users control over their privacy, Facebook has launched "Off-Facebook Activity" on January, an initiative originally announced last August. This lets you view which businesses you've visited are sending data to Facebook, leading to targeted ads on the platform.
This explains why some items you've researched online appear on Facebook. This isn't limited to online websites you've visited, but mobile applications that you use with a Facebook login as well. The social network company also provided an entire page, explaining about this feature.
If you don't like the idea of online sites sending your data to Facebook, here's how to access Off-Facebook Activity.
First, in the upper right portion of the Facebook home page is the an arrow, click it.
Then hit Settings.
You'll be directed to a new page and from here. You'll want to click Your Facebook Information.
The right side of the page will change accordingly, and here you will find "Off-Facebook Activity."
Since you're already reading this article, here's a "one-click stop" to jump straight to the Off-Facebook Activity.
From here you can view websites that have interactions with Facebook, giving you a slightly broader sense with what data they collect. You can choose to turn off the activity from that particular site. You also have the bigger option to turn off all future Off-Facebook Activities.
If you want to remove all previous data saved by Facebook, "Clear History" was announced by CEO Mark Zuckerberg during 2018's F8 conference. This should erase stored data that Facebook received outside of their platform.
If you want to head for the extra mile, you can check out your Ad Settings. This gives you the option to restrict data collection from Facebook's partners. All you have to do is choose the "Not Allowed" option.