Instantbird is an instant messaging application with close ties to Mozilla. These pages document Instantbird and also provide links to documentation about the Chat Core backend which is also used in Thunderbird.
Instantbird is built on the same technical platform as Firefox. Originally proposed as a Google Summer of Code project to create an XUL interface around libpurple (the backend of Pidgin). Instantbird was not accepted, but was started anyway in 2007, it has since grown beyond being a simple frontend for libpurple to having protocols of it's own.