It`s not just facebook though, your computer stores small files called cookies that hold information about websites you`ve visited & searches you`ve done. Websites display adverts of things you may be interested in based on your cookies.
A bit more info from here -
https://support.google.com/adsense/t...054008269&rd=1
"Google shows you ads based on many factors, including:
Types of websites you visit, and mobile apps you have on your device
Cookies on your browser and the settings in your Google Account
Websites and apps you’ve visited that belong to businesses that advertise with Google
Your activity on another device
Previous interactions with Google’s ads or advertising services
Your Google Account activity and information"
Disabling cookies in your browser settings will help to stop them.