The best revenge would be to call your local health department and your state's consumer affairs department. Don't bother with the theft issues but explain in detail about the health code violations. Do not tell them that you were just fired! Tell them that you have a close friend that works there, or that the manager brags about getting away with the violations (if he does..). Then mention that you are thinking of calling the local TV stations about this. Find out if you can call back and find out how the inspection went. Usually this type of info is public, but you may have to dig for it. Once they do the inspection and you have the information, email it (if it is bad) to your local papers and TV stations. One of my area stations has a news segment called "DIRTY DINING". Check to see if any of yours have something like this or any consumer rights reporters. Also, if you really want to get satisfaction, make copies of the report and place them under the windshield wipers of the cars in the parking lot. You can not be sued by the restaurant if it is correct and public information. (Don't add any accusations about the theft - only health dept info.)
Then, after this hits the fan, get ready to mail (NOT email) a note containing the health dept info and a general statement about the theft (like "we all know he steals money and gives away free pizzas for trade"). Mail this to the parent company - not to the franchise owner. I've seen owners hire relatives as managers and/or cover up problems so that companies do not fine or pull the franchise. Do not mention too many details and do not complain about specifics or being fired.
Keep in mind one thing. This may or may not effect your ex coworkers. If you are concerned about this then skip the TV, papers and parking lot notes. Let the company do something about it and if they don't just let it go and have one of your friends pose as your manager on any future applications that you submit for jobs.