From CNET:
Facebook can track you across the web. Here’s how to stop it
If you haven’t been using the privacy feature Facebook introduced last year, now’s the time to start. It’s called Off-Facebook Activity and it lets you see and control data that apps and websites share with the platform — and monitor the kind of information third-party apps can access.
With the privacy feature, you can clear the history of apps and websites that have shared your data. You can also turn off future Off-Facebook activity, which tells Facebook to disconnect any information the company has shared from your account. Or you can selectively choose which companies you want to stop sharing your activity and it’ll stop showing you those targeted ads.
Here’s how to get a better grip on your Facebook privacy.
© Provided by CNET The Facebook tool allows you to control which sites share your information. Facebook
Using Facebook’s business tools, you can see what information apps and websites have sent to the company. From there, you can clear the information from your account and turn off future “off-Facebook activity” from your account. You’ll be able to control this for all apps and websites so they’ll no longer be able to share your search activity with Facebook.
To get started, go to Settings & Privacy > Settings > Your Facebook Information > Off-Facebook Activity. From there, you can manage your Off-Facebook Activity, clear all history and turn off any future activity to your account.
What happens when you turn off activity managed by Off-Facebook
Once you clear the activity managed by the tool, Facebook will remove your identifying information that the apps and websites share. That means Facebook won’t know which websites you visited or what you looked at, so you won’t see any targeted ads from those sites.
What else you can do to improve your privacy on Facebook