According to the standard RM rules, if you learn the list Light Law, you have to learn 2 different Directed Spell skills, one for Shock Bolt, and one for Lightning Bolt. The spells are similar, but the core rules says you learn one skill for each. (yes, there are options that say otherwise, but the official ruling goes by the core).
The second paragraph above was saying that the Froststaff, Firestaff, & Thunderstaff spells would follow the same pattern. One list, three different Directed Spell skills because these are different directed attacks.
As for mark's question, the answer is no, you cannot use "Directed Spell: Firebolt" skill with the Firestaff spell. The spells are different, and while the end results are similar, they are not the same spell.
A Shock Bolt from one list is the same as a Shock Bolt from any other list in terms of how it works. A Firebolt is not the same as a Firestaff.
Again -- remember that the Official Ruling given above pertains to the core rules!!! If you are using any options that affect/change the core rules involved in the Ruling, then you need to consider the impact of the option being used on the Ruling.