You must first be a foreigner legally living in Mexico for at least five years. It's getting through those first five years that's the sticky part... after that it's rather easy compared to most other countries.
http://www.banderasnews.com/0508/nb-mexcitizen.htmPuerto Vallarta - When you have been living in Mexico for 5 years, you may qualify for Mexican Citizenship. There are benefits in being a Mexican Citizen, but there are also a few drawbacks or limitations. Mexican Citizens cannot legally drive (or own) a vehicle that has foreign license plates. If you have a vehicle that you are strongly attached to, citizenship is not for you.
On the plus side, Mexican citizens have lots of advantages. They can own land, for example. While visitors have to use a bank trust, Mexican citizens can own property in their own names without having to use a bank trust. Mexican Citizenship also means that you don't have to make the annual trip to the local immigration office to renew your FM-3.
There are other advantages, too. Certain jobs and businesses have restrictions, wherein only Mexican citizens can hold those jobs or own those businesses. You may not want to drive a taxi, or own a corner taco stand, but as a citizen it's an option. Mexican Citizens can vote. While I've never been politically minded, a Mexican voter registration card is better identification than a passport when cashing checks or dealing with government agencies.
Becoming a Mexican citizen is comparatively easy. You fill out a form, submit it with a copy of your existing passport and FM-3 or FM-2, along with some photos, pay a fee, and wait. In a few months, you will have to pay a second fee, and sign some additional documents. Again you have to wait a few months. Finally you'll get the call to pick up your Certificate of Naturalization, at which point you'll have to surrender your FM-3 or FM-2. At that time, you can also apply for, and receive, your Mexican passport.FM-2 (long term resident) and FM-3 (one year resident) status is granted (or not) through Mexico's Immigration department. Acquiring a work permit is separate and that is also granted (or not) by Mexico's Immigration department. In order to legally reside and/or work in Mexico for the first five years in order to eventually become a citizen, one still has to go through Immigration.
Your scenerio makes it seem that I - as a resident of the USA who has never even been to Mexico - can simply apply for Mexican citizenship tomorrow, and it would automatically be granted... there is simply no way that could happen.