Use Discoverly to see any mutual Facebook friends you have with your LinkedIn connections (or potential connections).
After you connect Discoverly with your LinkedIn account and install a Chrome extension, you will see a little icon next to a connection’s photo. Hover over that graphic to view any mutual Facebook friends. This can be a great thing to mention when you first reach out to someone on LinkedIn, or better yet see if someone you both know from Facebook might be willing to make a personal introduction.
It also works with Twitter (look for the icon next to the person’s name when you are on their page on the main Twitter site).