var aCharset = "Big5"; //這裡改成您偏好的編碼!
var winMgr = Components.classes['@mozilla.org/appshell/window-mediator;1'].getService();
var winMgrI = winMgr.QueryInterface(Components.interfaces.nsIWindowMediator);
var topwin = winMgrI.getMostRecentWindow("navigator:browser");
var b = topwin.document.getElementById("content");
var c = b.docShell.QueryInterface(Components.interfaces.nsIDocCharset);
if (b.originCharset) {
   aCharset = b.originCharset;
   delete b.originCharset;
} else b.originCharset = c.charset;
if (c.charset.toUpperCase() != aCharset.toUpperCase()) {
   c.charset = aCharset;
   b.webNavigation.reload(nsIWebNavigation.LOAD_FLAGS_CHARSET_CHANGE);
}