There were an browser addon which showed message when someone from Facebook unfriended you. However now it is dead. Is there any alternative to track my friends?
There may not be any addon which does the job but there are several userscripts which you can use. Here is a list of few of them :
There are serveral others available at userscripts.org.
To install a userscript you will need Greasemonky installed. It is available both as an addon for Firefox and extension for Chrome.
Try each one out to see which one work out best for you.