One other thing you can do before grabbing the extinguisher, if you have any doubts but want to try to make a save.
Pick up your phone, dial 911, when the operator askes what you emergency is, simply say "FIRE" and set the phone down. Do not hang it up, leave the line open. There will be help coming and on it's way in a brief moment.
Today's technology has brought us enhanced 911 to most areas, when you call populates on the 911 dispatcher's computer screen, it should tell her who you are and your adress, along with many many other things.
Now, by chance all you have is a cell phone, I'll offer this advice too as it may be slightly different. Contact your local LEO agency that runs the 911 service in your area. Ask them if they can put your cell number into their system, along with your name and address for emergency purposes. Just remember after doing this, you do not want to prank the 911 operators.