Right now, Firepower is some arbitrary measure that nobody is sure how to calculate. I propose normalizing it against unit caps, since there's an assumption that units have a certain balance of firepower at their caps. This will be adjusted by mark level.
A mark 1 fighter, bomber, frigate, or any other ship with cap 98 at mk1 will be normalized to 1 firepower. Higher mark ships will multiply their firepower by their mark level, so a mark 5 fighter will show up as 5 firepower.
Ships with a cap different than 98 will divide standard cap (98) by their cap, so deflector drones will show up as something like 2/5 of a unit of firepower each, so a mark 5 deflector drone will show up as 2 units of firepower. Stealth Battleships (I believe their mk1 cap is something like 5?) will show up as 20 units of firepower, with mk5 showing up as 100 units of firepower.
In fleet engagements, this will allow players to more accurately gauge just how dangerous an enemy force is, since it's normalized to if a player were facing a certain number of mk1 fighters, bombers, and frigates. The typical mk5 force will show up as 5 times more dangerous than the typical mark 1 force - which is exactly how much more dangerous it is, since damage, armor, and hitpoints are all scaled by (mark 1 stat)*(ship mark).
Starships will probably show up as 50 firepower * mark, spirecraft 200 or 250* mark, and golems something like 1500.