http://developer.mozilla.org/en/docs/Building_an_Extension -tut
http://kb.mozillazine.org/Getting_started_with_extension_development -tut
http://ted.mielczarek.org/code/mozilla/extensionwiz/ - Wizard generates an extension skeleton
Extensions add new functionality to Mozilla applications such as Firefox and Thunderbird. They can add anything from a toolbar button to a completely new feature. They allow the application to be customized to fit the personal needs of each user if they need additional features, while keeping the applications small to download.
Extensions are different from plugins, which help the browser display specific content like playing multimedia files. Extensions are also different from search plugins, which plug additional search engines in the search bar.
Documentation
Extension Frequently Asked Questions
Common questions and answers about extension development.
Setting up extension development environment
A few essential setup tips that make extension development easier.
Extension Packaging
How to package your Firefox extension for downloading and installation.
Creating Custom Firefox Extensions with the Mozilla Build System
How to set up the build environment for an extension that makes use of binary components.
Updating extensions for Firefox 3
Lists the known changes in Firefox 3 that affect extensions with pointers to the relevant documentation.
Code snippets
Code commonly used by many extensions. See also articles in Category:Extensions for more examples.
Installing extensions
How to programmatically install extensions.
Submitting an add-on to AMO
How to distribute your add-on using the AMO web site.
