Providing Command-Line Options

This is an archived page. It's not actively maintained.

Extensions and XUL applications can modify the way command line parameters are handled by writing a component that implements the nsICommandLineHandler interface and registering it in a category.


The code below is an example of writing a JavaScript XPCOM component to handle command line parameters.

You can learn more about how the command line is interpreted by looking at the documentation for the nsICommandLine interface.


The below example component implements two command line parameters:

firefox.exe -myapp
Opens a chrome window for My Application.  
firefox.exe -viewapp url
Opens a chrome window for My Application and passes it an nsIURI object.

Using the example

To use this sample code, save the commandLine.js file into the components directory and add the following lines to your chrome.manifest file:

component {2991c315-b871-42cd-b33f-bfee4fcbf682} components/commandLine.js
contract;1?type=myapp {2991c315-b871-42cd-b33f-bfee4fcbf682}
category command-line-handler m-myapp;1?type=myapp

The JavaScript code

const Cc = Components.classes;
const Ci = Components.interfaces;


// CHANGEME: to the chrome URI of your extension or application
const CHROME_URI = "chrome://myapp/content/";

 * Utility functions

 * Opens a chrome window.
 * @param aChromeURISpec a string specifying the URI of the window to open.
 * @param aArgument an argument to pass to the window (may be null)
function openWindow(aChromeURISpec, aArgument)
  Services.ww.openWindow(null, aChromeURISpec, "_blank",

// Command Line Handler
function CommandLineHandler() {

CommandLineHandler.prototype = {
  classDescription: "myAppHandler",
  // CHANGEME: generate a unique ID
  classID: Components.ID('{2991c315-b871-42cd-b33f-bfee4fcbf682}'),
  // CHANGEME: change the type in the contractID to be unique to your application
  contractID: ";1?type=myapp",
  _xpcom_categories: [{
    category: "command-line-handler",
    // CHANGEME:
    // category names are sorted alphabetically. Typical command-line handlers use a
    // category that begins with the letter "m".
    entry: "m-myapp"

  QueryInterface: XPCOMUtils.generateQI([

  /* nsICommandLineHandler */
  handle : function clh_handle(cmdLine)
    try {
      // CHANGEME: change "viewapp" to your command line flag that takes an argument
      var uristr = cmdLine.handleFlagWithParam("viewapp", false);
      if (uristr) {
        // convert uristr to an nsIURI
        var uri = cmdLine.resolveURI(uristr);
        openWindow(CHROME_URI, uri);
        cmdLine.preventDefault = true;
    catch (e) {
      Components.utils.reportError("incorrect parameter passed to -viewapp on the command line.");

    // CHANGEME: change "myapp" to your command line flag (no argument)
    if (cmdLine.handleFlag("myapp", false)) {
      openWindow(CHROME_URI, null);
      cmdLine.preventDefault = true;

  // CHANGEME: change the help info as appropriate, but
  // follow the guidelines in nsICommandLineHandler.idl
  // specifically, flag descriptions should start at
  // character 24, and lines should be wrapped at
  // 72 characters with embedded newlines,
  // and finally, the string should end with a newline
  helpInfo : "  -myapp               Open My Application\n" +
             "  -viewapp <uri>       View and edit the URI in My Application,\n" +
             "                       wrapping this description\n"

var NSGetFactory = XPCOMUtils.generateNSGetFactory([CommandLineHandler]);