Facebook has matured into a place where you can meet and keep in touch with old and new friends. Even in this cyberworld, friendships can fall apart. That’s where the Unfriend Notify comes in handy. Unfriend Notify is a free extension for Chrome and Firefox that alerts you when someone has unfriended you on Facebook. Without a 3rd party solution like this, there is no clear cut way to tell when you have been unfriended. Currently the only way to find out, is to browse through your friend list to see if the person is still there. Or, you can search for that specific person within your friends list to see if they’ll still show up. Both of these options are time consuming and inconvenient.
When you install the Unfriend Notify extension, a “Lost Friends” link is placed at the top of your friends list. The link will update with a number each time someone has unfriended you. An alert is also sent out to you if you happen to have your browser open at the time your friend un-follows you.
Source: Addictive Tips