The act of getting two of your Facebook friends from unrelated social circles to "friend" one another based on compatibility and/or complimentary facets of their personalities for their mutual benefit/support. Typically accomplished through friend suggestions to both friends for the other, or both friends interacting with your Facebook page and friending one another. Derived from the term, cross-pollinate.
My best friend from college and one of my co-workers would really hit it off. I should cross-friend them.