How to remove ‘wordpress…’ text from page titles in tabs

this string is displayed when you get a nonce mismatch, something that should not happen much under normal usage. If it does haen enough to make you aware to it then you should investigate the cause.

Anyway, no easy filter for that string so you will have to use the translation api to replace it.

add_filter ( 'gettext', 'wpse_120304', 10, 3 );
function wpse_120304($translated, $original, $domain) {
  if ($original == 'WordPress Failure Notice')
    return 'Failure Notice'; // or something else
  else
    return $translated;
}

or just use the “say what” plugin http://wordpress.org/plugins/say-what/ from which I have lifted the idea to this piece of code.