Thank you Ryan. The fix works now in Firefox. Case is closed I hope.
I discovered something new. I get the error if I use Firefox. I reinstalled FF and it happened the same. If I open Opera or IE the page works fine.
Oh, yes. Thanks for asking. I use the bookmark to login to the dashboard in my two blogs.
http://pakalahau.wordpress.com/wp-login.php?loggedout=true
http://darkvotum.wordpress.com/wp-login.php?loggedout=true
Both are getting the 403 Forbidden Error with a small letter nginx below the error. I tried to delete cache and cookies but nothing.
