Firearms and Weapon Focus?

[Kor - Orc Scrollkeeper]

In the Campaign Setting (pg 212) it is noted that Exotic Weapon Proficiency (firearms) grants proficiency with all firearms.

Would the Weapon Focus feat be taken with a specific firearm, or with the whole category?

Weapon Focus (Musket) vs Weapon Focus (firearms)

[Vorpal Bored]

As it states in the SRD it would apply to one specific firearm of choice, such as a musket.

The feat may be taken multiple times, each time applying to a new and specific weapon.

[James Jacobs]

Correct; while you can get all firearms for one proficiency, being super awesome at one takes specific feats. Feats like Weapon Focus, Weapon Specialization, and Improved Crit still require you to pick a specific single weapon.