var pi = Components.classes["@mozilla.org/profile/manager;1"].getService(Components.interfaces.nsIProfile);

for(key in Components.classes) {
  print(key);
}



var ext = Components.classes["@mozilla.org/extensions/manager;1"]
                    .getService(Components.interfaces.nsIExtensionManager)
                    .getInstallLocation("ec8030f7-c20a-464f-9b0e-13a3a9e97384")
                    .location; 
print(ext);