You can find that by going through these steps:
- hover your cursor over the "Community" tab
- click on the "Friend Feed" entry from that dropdown menu
- you'll now be on the "My Friend Feed" page
- click on the "Settings" link on that page
- you'll now be on the "My Friend Feed Settings" page
- the "mutual friends" link is just under that page heading
Let me know if you have any trouble with my directions.
Have a good day!