When cache is empty the favicon is point to
http://site url/favicon.ico and ask for username and password for intranet site. finally 404 file not fount.
After re-fresh it works properly and loads the favicon from masterPage.
In master page I am using
<SharePoint:SPShortcutIcon runat="server" IconUrl="/_catalogs/masterpage/favicon.ico" />
similarly, for CSS files, it shows
401 unauthorized when cache is empty. After reload it works properly.
Thanks in advance for help.