nsIBlocklistService in Firefox 3.0

 Determine if an item is blocklisted
 @param   id
          The GUID of the item.
 @param   version
          The item's version.
 @param   appVersion
          The version of the application we are checking in the blocklist.
          If this parameter is null, the version of the running application
          is used.
 @param   toolkitVersion
          The version of the toolkit we are checking in the blocklist.
          If this parameter is null, the version of the running toolkit
          is used.
 @returns true if the item is compatible with this version of the
          application or this version of the toolkit, false, otherwise.