Plugins, Extensions, and TweaksEdit
- PluginDoc — Lists common plugins and how to install them in Firefox.
- Mozilla Addons — Official Mozilla site for plugins, extensions and themes.
- Addonsmirror.net — unofficial extension database (Formerly extensionsmirror.nl)
- Firefox Tweak Guide — Has some great tweaks for speed and various other customizations.
- How to write Firefox extensions — Tutorial for creating Firefox extensions, which includes a "Hello, world!" extension to explain the basics.