When might Facebook read the cookies on my computer or device?
Web browsers send any cookies for a particular web domain (ex: facebook.com) to the website each time a machine with those cookies accesses content served from that domain. This means that any facebook.com cookies will be sent to Facebook when any page is accessed at facebook.com. It also means that these cookies are sent to Facebook when someone accesses a third-party website that has a connection to facebook.com, like through one of our plugins.
Sometimes we work with websites, apps and their partners so that we can place or read Facebook cookies on your browsers or devices. This allows us to do things like read and reference cookies from more than one device or browser that you use so we can provide you Facebook services across all of your devices and improve and understand the products, ads and services we offer to you and others. Your browser or device may allow you to block these technologies, but you may not be able to use some features on Facebook if you block them.