qulacuno sa come si usa il codice

codice:
(Components.interfaces.nsIWebNavigation);
var docShell = navigator1.QueryInterface(Components.interfaces.nsIDocShell);
docviewer =
docShell.contentViewer.QueryInterface(Components.interfaces.nsIMarkupDocumentViewer);
docviewer.fullZoom = 97%;");
browser.execute("var navigator1 =
window.QueryInterface(Components.interfaces.nsIInterfaceRequestor).getInterface
codice:
var zoom = 97%;
 var docViewer = gBrowser.selectedBrowser.markupDocumentViewer;
 docViewer.fullZoom = zoom;
 }
Per modificaRE lo zoom con mozilla?