Hi Eric,
If its not clear then its not a stupid question :)
The Firefox plugin is open source and available on GitHub:
https://github.com/mozmark/ringleaderHowever its not much use on its own - you need another tool for it to interact with.
OWASP ZAP would be a good tool to start with (ok, I'm biased as I'm the ZAP project lead;). It comes with Plug-n-Hack 'built in' and includes the Firefox addon. Just click on the 'Plug-n-Hack' button on the ZAP 'Quick Start' tab.
I demoed driving ZAP from Firefox using PnH at AppSec USA in New York - the video is available here:
https://www.youtube.com/watch?v=pYFtLA2yTR8Let us know if you have any problems with it.
Simon