Imagine standing at the fire line with the sun beating on your head at 100 degrees and wood/trees exploding in front of you at 572 degrees, the flashpoint of wood. A simple campfire produces about 1100 degrees F. There are many other dangers such as falling trees, flying ambers and, not to forget, the air the fire fighters breathe.
After giving some thought to those few points, and still having a home to go back to after evacuation, simply saying Thank You Firefighters does not seem quite sufficient. In the military the soldiers are awarded flight pay, jump pay, hazardous duty pay and combat pay. One appropriate gesture would be to pay the firefighters on the fire line double time from the time they are deployed to the time they are relieved.
We, the people, collectively benefit from their dangerous mission(s) and it logically follows that collectively we should reward them generously.