Stealther is an extension that leaves no trace of where you were or what you were doing. Stealther disables the following items:
- Disk Cache
- Saved Form Information
- Referrer Header
I guess you could say this takes paranoia to a whole new level.
The one drawback was the installation. You need to download the xpi and install it manually as opposed to Firefox detecting and installing the extension automatically. Most users will have a problem with this.
Since experienced Firefox users already know about how to enable (or disable) these types of settings(coughcoughabout:configcough), Stealther is primarily for users who are new to Firefox and need a quick way to cover their tracks.