This tutorial explains how to create a toolbar extension for the Firefox web browser (specifically for version 1.5 and later). It provides an overview of how extensions are developed, the tools required to create an extension, and details on how toolbars are created. Please note that this tutorial is lengthy; I recommend spending time with it over the course of a few days (it makes for a good weekend read).
This document describes the Aviary Toolkit's new preferences system. Using this system it is possible to create preferences windows that display and operate appropriately on various platforms (Windows, MacOS X and GNOME).
This article provides helpful information to extension developers trying to update their extensions to work properly in Firefox 3.6.