On Firefox 4, users can install and uninstall Jetpack extensions without a browser restart. The traditional extensions are needed for a browser restart.

Screenshot: DOM Inspector will be disabled after you restart Firefox.
Traditional extensions will be disabled after you restart Firefox.

Jetpack is not required

Jetpack itself does not provide the restart-less feature. Jetpack SDK is a rich development environment for Restart-less extensions (which are called by Bootstrapped extensions).

To make a bootstrapped extension, you need:

  1. add the em:bootstrap="true" in install.rdf; and
  2. add bootstrap.js

Hello world of bootstrapped extensions

Step1. Write install.rdf with em:bootstrap="true"

There is no difference from traditional extensions... Only one exception is to add em:bootstrap="true". 

<?xml version="1.0" encoding="utf-8"?>
<RDF xmlns="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
     xmlns:em="http://www.mozilla.org/2004/em-rdf#">
  <Description about="urn:mozilla:install-manifest">
     <em:id>bootstraptest@cat-in-136.blogspot.com</em:id>
     <em:version>1.0</em:version>
     <em:type>2</em:type><!-- extension! -->
     <em:bootstrap>true</em:bootstrap>

     <!-- Firefox -->
     <em:targetApplication>
        <Description>
            <em:id>{ec8030f7-c20a-464f-9b0e-13a3a9e97384}</em:id>
            <em:minVersion>4.0b5</em:minVersion>
            <em:maxVersion>4.0</em:maxVersion>
        </Description>
     </em:targetApplication>

     <em:name>bootstraptest</em:name>
     <em:description>bootstraptest</em:description>
     <em:creator>@cat_in_136</em:creater>
     <em:iconURL/>
     <em:optionsURL/>
  </Description>
</RDF>
Step2. Write bootstrap.js

This file shall contains entry point functions : install(data,reason), startup(data,reason), shutdown(data,reason) and uninstall(data,reason). 

function install(data, reason) {
}

function startup(data, reason) {
    var prompts = Components.classes["@mozilla.org/embedcomp/prompt-service;1"]
                    .getService(Components.interfaces.nsIPromptService);
    prompts.alert(null,
                  "Startup!",
                  "Hello world.");
}

function shutdown(data, reason) {
    var prompts = Components.classes["@mozilla.org/embedcomp/prompt-service;1"]
                    .getService(Components.interfaces.nsIPromptService);
    prompts.alert(null,
                  "Shutdown!",
                  "Good bye.");
}

function uninstall(data, reason) {
}

This extension says "Hello world." after it is installed and/or enabled, and "Good bye." after it is uninstalled and/or disabled.

Above code is very very simple. bootstrap.js in the general bootstrapped extensions (for example Jetpack) are complexity.

Step3. Packaging

All you have to do is compress the files. 

$ zip -9r ../bootstraptest.xpi *
  adding: bootstrap.js (deflated 66%)
  adding: install.rdf (deflated 54%)
$

Open the XPI file to install. As soon as it is installed, a following dialog is displayed.

"alert message : 'Hello world.'"

See also