In a nutshell, Chrome is the user interface of Mozilla products. The user interface is composed mostly of [[XUL]], [[XBL]], CSS, and JS files. Extensions are (usually) chrome applets. 90% of You can make changes to these files without needing to recompile the Mozilla project you're working on - which is an [http://developer.mozilla.org/en/docs/Extensions extension]enormous timesaver, typically is chromeespecially for people who are just starting out on Mozilla-based development).

In If you look in the XUL worldchrome subdirectory of your installation, Chrome is you'll find .jar files - these contain the chrome files that make up the top level window which contains groups of UI elements of various typesuser interface. Example of chrome These jar files are the browser window and dialog windowactually just ZIP archives. The Extensions are (usually) chrome obtains its UI description from four types applets. 90% of providersan [http: //developer.mozilla.org/en/docs/Extensions extension], typically is chrome.

Acoording to WierdAl (#developers), Firefox uses the toolkit approach: [http://developer.mozilla.org/en/docs/chrome.manifest Chrome Registration - MDC] whereas SeaMonkey uses the old way (xpfe). ==Code Registry Example==<pre>1. content necko jar:comm.jar!/content/necko/ xpcnativewrappers=yes2. locale necko en-US jar:en-US.jar!/locale/en-US/necko/3. content xbl-marquee jar:comm.jar!/content/xbl-marquee/4. content pipnss jar:pipnss.jar!/content/pipnss/5. locale pipnss en-US jar:en-US.jar!/locale/en-US/pipnss/6. # Firefox-only7. overlay chrome://browser/content/pageInfo.xul chrome://pippki/content/PageInfoOverlay.xul application={ec8030f7-c20a-464f-9b0e-13a3a9e97384}8. overlay chrome://communicator/content/pref/preftree.xul chrome://pippki/content/PrefOverlay.xul9. overlay chrome://navigator/content/pageInfo.xul chrome://pippki/content/PageInfoOverlay.xul application=seamonkey@applications.mozilla.org10. content pippki jar:pippki.jar!/content/pippki/ xpcnativewrappers=yes11. locale pippki en-US jar:en-US.jar!/locale/en-US/pippki/12. content global-platform jar:toolkit.jar!/content/global-platform/ platform13. skin global classic/1.0 jar:classic.jar!/skin/classic/global/14. override chrome://global/content/netError.xhtml jar:embedder.jar!/global/content/netError.xhtml15. content inspector jar:inspector.jar!/content/inspector/ xpcnativewrappers=What no</pre> *Line 1: <pre>content packagename uri/to/files/ [flags]</pre>**This code will register the package called necko when resolving the URL jar:comm.jar!/content/necko/ with the xpcnativewrappers flag on   *Line 5: <pre>locale packagename localename uri/to/files/ [flags]</pre>**This code will register a locale package called pinpnss with the localename en-US when resolving the URL jar:en-US.jar!/locale/en-US/pipnss/**NOTE: If there are more than one locale file register for the package, chrome will select the best-fit locale for the URL.  *Line 6: <pre># this line is a comment - you can do put whatever you want here</pre>**To comment your code, put '#' in the beginning of the line.  *Line 7: <pre>overlay chrome://URI-to-be-overlayed chrome://overlay-URI [flags]</pre>**The prupose of this code is to overlaying one chrome on top of the other. The application={ec8030f7-c20a-464f-9b0e-13a3a9e97384} is a flag that specific which application will have this overlay.  *Line 13: <pre>skin packagename skinname uri/to/files/ [flags]</pre>**This will register a skin package gobal with the skinname classic/1.0 when resolving the URL jar:classic.jar!/skin/classic/global/**NOTE: If more than one skin register for the package, chrome will select the best-fit skin for the URL.  *Line 14: <pre>override chrome://package/type/original-uri.whatever new-resolved-URI [flags]</pre>**The purpose of this is to override a chrome file provided by the application or XULRunner with a new extension or embedder.  =Additional Info= ==Starting Out==WierdAl in #developers said he started doing the development work by obtaining [http://www.gerv.net/software/patch-maker Gerv's Patch Maker] and looking in Bugzilla for a bug with the words "good first bug" in the Status Whiteboard. WierdAl also has a blog on his development: *[http://weblogs.mozillazine.org/weirdal/archives/cat_xul_widgets.html Burning Chrome: XUL Widgets Archives]*[http://weblogs.mozillazine.org/weirdal/archives/cat_xul_xbl_js_and_dom.html Burning Chrome: XUL, XBL, JS and DOM Archives] == ChromeTutorials==Here are the following examples of what you can do with tutorials on how to create user interface parts using Chrome:

http://developer.mozilla.org/en/docs/Working_with_windows_in_chrome_code http://developer.mozilla.org/en/docs/Chrome_Registration [http://www.xulplanet.com/tutorials/xultu/chromeurlintro.html1.1 Introduction]