A friend emailed a document which he received from a friend, so I have no idea where it originated, but it outlines the new procedures for renewing a non-working FM-3 which were instituted at Migración on 1 May. Some things you will be able to do online before visiting an INM office.
The document lists everything you'll need and provides step by step instructions for filling out forms as well as sample letters to submit.
The following is a large Adobe Reader document; if you don't have Reader installed on your computer, you can download it here.
