It's far from clear there was an active firefight. There was a report of a single gunshot after the fire started, and multiple rounds cooking off in the fire.
From what I've gathered there were few shots fired before that, and it's not even clear if they were police or Dorner.
If you listen to the scanner feed at post #59 it's clear that there were no shots being fired even while the front door was being pried open. The door prier-opener reported blood splatter inside.
No shots are being fired, they know the occupant is injured, and at that point they decide to "deploy the burners as planned".
How?