What is Chrome?
Chrome is the user interface parts of the application window that are outside of a window's content area. [ Toolbars, menu bars, progress bars, and window title bars are all examples of elements that are typically part of the chrome.
Chrome Registration
A supplier of chrome for a given window type (e.g., for the browser window) is called a chrome provider. The providers work together to supply a complete set of chrome for a particular window, from the images on the toolbar buttons to the files that describe the text, contents and appearance of the window itself.
There are three basic types of chrome providers:
Content
The main source file for a window description comes from the content provider, and it can be any file type viewable from within Mozilla. It will typically be a XUL file, since XUL is designed for describing the contents of windows and dialogs. The javascript files that define the user interface are also contained within the content packages, as well as most XBL binding files.
Locale
Localizable applications keep all their localized information in locale providers. This allows translators to plug in a different chrome package to translate an application without altering the rest of the source code. The two main types of localizable files are DTD files and java-style properties files.
Skin
A skin provider is responsible for providing a complete set of files that describe the visual appearance of the chrome. Typically a skin provider will provide CSS files and images.
What you can do with Chrome
Here are the following examples of what you can do with Chrome: