"The QC Cast on Twitter" http://www.questionablecontent.net/twitter.php URL's on the various pages at http://www.questionablecontent.net/contact.php, http://www.questionablecontent.net/ (bottom of each comic) and probably other places does not work.
Also, why the extra small font in the latest comic? :/
No one here in the forum has any involvement in the comic web site or Jeph's other accounts. The cast twitter was a side joke which he has long given up on. You can contact Jeph using the details on the site's Contact page; he promises to read everything, but not to reply individually. He rarely looks at the forum.
And does the "Notify" button enable Email or Private Message notification?
Email. You can also set up email notification of PMs.