1) Wrong it is not illegal. 1a) You are already polluting the atmosphere thanks to the idiots at Firestone who didn't check their equipment readings before they let you go.
2)Absolutely correct, however you can rent an item called a vacuum pump and a set of gauges from your local Autozone, Advance, or Pep Boys and fix it yourself if you have 1/4 of a brain.
Ford AC systems are not that difficult or expensive to fix. First, you should check your hoses for signs of a leak. Most places like Firstone will have UV dye in their oil charges, but you should be able to see either oil or green looking oil on the hose if that is the cause of the leak. The most common place is where the hose converts from rubber to metal. If that passes the test- then great, you've avoided the second most expensive problem. The compressor is most likely ok also since it did work until the refrigerant ran out (coolant btw, runs through the radiator).
What you need to do is replace the O-rings. To do this you'll need a simple tool that costs about $10. I just went to check my lines and make sure that's still what Ford uses, but I can't see the connections. If it's still the same snap ring system as I'm familiar with, then that's the tool you'll need, it looks like some hat rings with the top cut out. You find the right size, then slide it in the back as far as you can, and then pull the hose apart. Once you get the hose disconnected, you'll notice 2 O-rings. Replace both of these rings. You can purchase O-ring kits specific to your vehicle, or purchase a large multi-kit. You will need to purchase special rings specifically for the compressor connection. This one should unbolt from the compressor, and will only fit on in one direction. The O-rings will be built into the compressor, and there will be flanges where the hoses fit into the compressor. Be sure that when you go to bolting it back on, you use your hand pressure to make sure that the hoses are in their appropriate flange before you go tightening down the bolt. Hold it down until you tighten it completely. If you get the hoses off the flanges, you will bend up the ends of the hoses.
You'll need to replace all the O-rings at the hoses, and remove the hoses from the Dryer located under the passenger fender. You might even have to physically remove the dryer itself to get to the O-ring on the other side.
Some where in the AC system, there is an orifice tube. Generally it's located in the high pressure (small line) near the evaporator. I wish I knew exactly where it was, it could be on the other side of the dryer, or in the high pressure line near the dryer. High pressure lines don't go to the dryer. Anyhow, look for a long straight metal section of hose with a connection point. When you disconnect this hose to replace the O-rings, look into the metal part of the hose with a flashlight- if you see some plastic thing in the line, use needle nose pliers or tweezers to remove the orifice tube. These generally cost about $4, but must be replaced if you're opening the system. It would just be dumb not to.
Also, be sure to check around the condenser for any line connections there to be sure you get all the O-rings.
Ok, now you've replaced all your O-rings and the orifice tube, you've gotten everything fixed up. It's time to vacuum the system. First make sure that the red high side hose is connected to a dummy connection at on the hose set and turned off. Connect the center line to the vacuum pump, and connect the low side line to the low side connector which is near the dryer. Now, be sure to read the directions that come with the vacuum pump before turning it on. There is a valve that you'll need to open partially when first starting to vacuum the system, then close to vacuum. Make sure that the low side line is open so it will vacuum your system. Once the vacuum pump is running, let it run for at least 30 mins. Look at the gauge, you should see a (-) or vacuum reading, let it go down as low as possible- which should be about -30 psi, maybe a little less. After 30 mins, cut off the low side hose valve, then the pump, now disconnect the line to the vacuum pump, and connect it to the gauges- there should be a place. Make sure it's tight. Open the valve on the low side, and note the reading on the gauge. Wait for at least 30 mins. Check the gauge again. If it has changed at all, then the system is not sealed. If you can't tell, wait a while longer. If you still don't notice any change, then the system is sealed.
When going to recharge, be sure to charge the oil first. Do not use any stop leak or oil charge with stop leak. Check the oil charge, but it's likely to be 2-3 oz. You'll also want to check your refrigerant charge, which is likely to be around 32 oz as a guess. Now, use the gauges to recharge the system, and watch the gauges while you are charging. It should be around 35 psi max while the compressor is on, and close to 50 when it's off.
Once you're done, you will have AC again.
Hang on a minute, I have to go look at a car, then I'll come back and find an article about recharging AC's which will help you.