Grapefruit enzymes reduce the amount of insulin that the body makes which helps the metabolism stay regulated. A well-regulated metabolism helps you to lose weight faster and more effectively. Scientists do acknowledge that grapefruit has properties that balance out blood sugar levels and help the metabolism.
It's possible your Facebook woes are coming from some sort of malware, be it a keylogger, a trojan, or some other type of virus. Even if you think your computer is clean, it can't hurt to check.
What you are seeing is known as Remarketing/Retargeting. This has been made possible on Facebook due to a service started by the company back in 2012 called Facebook Exchange (FBX) What is Facebook Exchange? It is an ad exchange started by Facebook in 2012.