One of my Weber kettles did the same thing, due to the same thing that caused you gasser to catch fire. Built up grease in the fire bowl.
1. You need to clean the built up grease off of any grill, gas or charcoal. Grills are NOT maintenance free.
2. Why the fark did you use a fire extinguisher on an outdoor grill? Close the lid and turn off the gas. Let it burn out. If you need to, wet down the area around the grill with water, so it doesn't catch fire. Never spray water directly on a grease fire, but you can close the lid and use a garden hose on the closed grill to cool the fire so it goes out on its own.
If your grill is not in a position to burn down the house or your deck, don't panic.
My neighbor called the fire department when his gasser caught fire. They shut off the gas valves and put it out with his garden hose.
Maintain your cooker, and it won't catch on fire. Plan ahead, and if it does catch on fire, you can put it out without a lot of drama and without ruining your grill.