Greasemonkey scripts for FB deletion.
Greasemonkey is a firefox addon, after installing it from addons.mozilla.org you can add any of these scripts to your greasemonkey
Please note that these scripts were design to function only on https://m.facebook.com , trying to run it on https://facebook.com simply won't do anything.
Update: Faceook have updated their mobile UI recently and the new UI wouldn't work with this script. To get back the old interface you need to install user agent switcher plugin (it would allow you to convince facebook that your webbrowser is very old so that they serve you the simple UI that we need.
I've found this user agent string Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.8) Gecko/20060110 Debian/1.5.dfsg-4 Firefox/1.5 to be working fine.
You know you are in old interface if it looks like this 
I've used this extension to change user agent.
If you are having difficulty, please feel free to open an issue. will be happy to help you.