Extensions are packaged and distributed in archive files (also known as Bundles), with the XPI (pronounced “zippy”) file extension. At a minimum, they contain an install.rdf, the chrome.manifest and a chrome/ folder. The chrome/ folder contains a content/ folder that contains the actual content files. These files contain the code that makes your extension actually do something. When this tutorial is finished, our extension will look like this:
myfirstext.xpi: //created in step 8
/install.rdf //created in step 3
/chrome.manifest //created in step 4
/chrome/
/content/
/content/myhelloworld.xul //created in step 5
/content/overlay.js //created in step 6
/chrome/locale/* //Building an Extension# Localization
/chrome/skin/
/defaults/preferences/ //Building an Extension# Defaults Files
Previously, it was possible to use the Add-On Packager tool to create the initial directory structure and some of the required files. This tool is no longer available.
The following tutorial pages will explain how to write each of these files (except locale/ and defaults/) and package them into an XPI (zippy) file. You can find information about the locale/ and defaults/ folders in the more general "Building an Extension" documentation.