Peekko Chat relies on a lot of technologies, which I'd like to cite here along with some excellent tutorials and documentation that I used to bootstrap myself on Firefox extension development. (Listed here in no particular order.)
UnrealIRCD - Easy to use IRC server
prototype - Awesome javascript library
JISIRC - A javascript IRC client
scriptaculous - A javascript library that can do a lot of incredible stuff. I'm only using it for unit testing currently.
Good documentation is worth its weight in gold.
Developer Notes for prototype.js by Sergio Pereira
IRC RFC by Christophe Kalt
HPSched Extension Tutorial by the Firefox Group in association with Georgia Institute of Technology
Born Geek Extension Tutorial by Jonah Bishop
Hello World Extension Tutorial by Brian Duff