Fire-building (1, W-1) (DSG) :
A character with fire-building proficiency does
not normally need a tinderbox to start a fire. Given some dry wood
and small pieces of tinder, he can start a fire in 2d20 minutes.
Flint and steel are not required. Wet wood, high winds, or other
adverse conditions increase the required time to 3d20 and a successful
Proficiency Check must be made to start a fire.
 

Fire-building (1, W+1) (WSG):
If a character with this skill makes a successful
Proficiency Check, he can start a fire without the use of flint and
steel or a tinderbox. If such a character does have the abovementioned
equipment, the time needed to start a fire is half as long as
it would be for a character without this proficiency. For more info
on building && maintaining fires, see the section on
Camping && Campfires.