To Find Who Unfriends You on Facebook:
1. Add Greasemonkey to your Firefox Browser from the addon homepage here.
2. After Installation restart the Firefox to active the add-on.
3. Now you can see the Greasemonkey smiling brown monkey head in the top-right corner of Firefox, next to the search bar.
Note: Chrome natively supports user scripts, so no need to install Greasemonkey on Chrome Browser.
4. Now simply Download Unfriend Finder Script on your browser. And install in in your browser to work with Facebook.
5. Go to your Facebook account, login with your user ID and Password. Now here you can see an additional option “Unfriends” on the upper right side of the Facebook window next to Home button.