function addEngine( name, ext, cat ) {

  if ( ( typeof window.sidebar == "object" ) && ( 
  typeof window.sidebar.addSearchEngine == "function" ) ) {

    window.sidebar.addSearchEngine( "http://www.tuosito.com/plugin/" + name + ".src", 
    "http://www.tuosito.com/plugin/" + name + "." + ext, name, cat );
  
  } else {
  
    alert( "I plugin di ricerca sono installabili solo in Firefox, 
    Mozilla e Netscape 6+." );
    
  }
  
}