Multiple item extension packaging

From the release of Firefox 53, multiple item extension packages are no longer supported and will not load. As a consequence, these packages are no longer accepted by AMO.

A multiple Item package provides the ability to package multiple installable bundles which can then be downloaded and installed by a user, or provided pre-packaged with an application or by an external program. Every multiple item package must provide an install.rdf file (not old-style install.js!) and has the same requirements as an extension except as noted below.

There is currently no feature to prevent or warn the user when installing an older version of an extension.

Multiple Item Package File Layout

The multiple item package file layout is a simplified form of an installable bundle and requires a file extension of xpi. A multiple item package may contain both extensions (e.g. xpi file extension) and themes (e.g. jar file extension). The basic structure is shown below:

/install.rdf                        Install Manifest
/extension1.xpi                     Extension
/extension2.xpi                     Extension
/theme1.jar                         Theme
/theme2.jar                         Theme
...

The Extension Manager will read the install.rdf Install Manifest to determine if this is a Multiple Item Package and then start the installation of the individual packages it contains automatically. No other files besides the install.rdf Install Manifest and the files with a jar and xpi file extension will be extracted or utilized.

install.rdf

A multiple item package does not have the same requirements as an extension for its install.rdf. The only required properties are em:id, em:targetApplication, and em:type.

For the Firefox and Thunderbird 1.5 Extension Manager to determine that the package is a multiple item package, the em:type specified in your install.rdf must be 32 and specified as <em:type NC:parseType="Integer">32</em:type>. The XML namespace xmlns:NC="http://home.netscape.com/NC-rdf#" must also be declared in your install.rdf as shown below.

...
<RDF xmlns="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
     xmlns:NC="http://home.netscape.com/NC-rdf#"
     xmlns:em="http://www.mozilla.org/2004/em-rdf#">
  <Description about="urn:mozilla:install-manifest">
    <!-- nsIUpdateItem type for a Multiple Item Package -->
    <em:type NC:parseType="Integer">32</em:type>
...

For the Firefox and Thunderbird 2.0 Extension Manager you can use the above syntax or <em:type>32</em:type> as shown below.

...
<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">
    <!-- nsIUpdateItem type for a Multiple Item Package -->
    <em:type>32</em:type>
...

When specifying em:targetApplication the minVersion specified should be the highest minVersion and the maxVersion specified should be the lowest maxVersion from all of the installable bundles contained by the multiple item package for the em:targetApplication. If this is not done, any items that are not compatible will not be installed unless a compatibility check discovers updated compatibility information.

Installation

Installation can be performed using any of the existing methods used for installing extensions / themes. The same user interface is used for installing a multiple item package (i.e. the individual packages contained in the multiple item package will not be listed). This also allows displaying of signing information for the multiple item package.

If a manager (e.g. extension / theme manager) is used, the manager will display the individual items contained by the multiple item package after the download completes in the same manner that it would if the user had chosen to install multiple individual items simultaneously. The manager will not display the multiple item package in the list of items after the download has completed.

Signing

All extensions now require signing by Mozilla. For multiple item packages, all internal add-ons need to be signed, but the container doesn't need to be signed. This means that the contained add-ons need to be submitted to AMO individually for signing. Additionally, the container add-on ID must not be the same as the ID of any of the contained add-ons.

Official References for Toolkit API

Official References. Do not add to this list without contacting Benjamin Smedberg. Note that this page is included from the pages listed below. So: Don't Add Breadcrumbs!

Structure of an Installable Bundle: describes the common structure of installable bundles, including extensions, themes, and XULRunner applications
Extension Packaging: specific information about how to package extensions
Theme Packaging: specific information about how to package themes
Multiple-item Extension Packaging: specific information about multiple-item extension XPIs
XUL Application Packaging: specific information about how to package XULRunner applications
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