If you are one those firefox users who want to clean all the traces of your browsing history, then let me tell you there is very simple way to do it with firefox itself without any extension.
here is how you can automate the cleaning of your browsing history and cookies..
1. Open Firefox
2. go to File Menu >> Tools >> Options , click on privacy tab
3. check the option which says: Always clear my data when I close firefox (as shown in the image below)