nsIAddonInstallListener in Firefox 3.0

 Called at the end of an add-on compatibility check. The status will be one
 of the results from nsIAddonUpdateCheckListener to indicate whether new
 information was found or not.
 @param   addon
          The add-on that is having its compatibility checked
 @param   status
          The status code from nsIAddonUpdateCheckListener for the update
          operation

 Called when an add-on compatibility check starts. This will be called 
 during an install if an add-on is incompatible according to it's
 install.rdf.
 @param   addon
          The add-on that the compatibility check will be for

 Called when an add-on download is complete. This will be called for every
 add-on downloaded.
 @param   addon
          The add-on that finished downloading

 Progress occurred in the download operation. This will be called multiple
 times during the download of an add-on.
 @param   addon
          The add-on that progress occurred for
 @param   value
          The value of the current progress
 @param   maxValue
          The maximum value |value| can reach

 Interface for handling download and install progress notifications for
 add-ons.


 Called when an add-on download starts. This will be called for every add-on
 downloaded including those started by an add-on update.
 @param   addon
          The add-on that is being downloaded

 Called when an add-on install completes. The status will be 0 on success.
 any other value constitutes a failed install.
 @param   addon
          The add-on that finished installing
 @param   status
          The status of the installation from nsInstall.h

 Called when there are no more add-on downloads or installs in progress.

 Called when the extension manager starts to install an add-on either
 through a call to installItemFromFile or from a webpage triggered install.
 @param   addon
          The add-on being installed