How do black firebombs differ from regular firebombs?

Black firebombs cost 500 souls whereas the regular ones cost 50. The black variety supposedly does "more damage" than the regular ones, but I can't find any information on how much damage either variety does and how/if they scale with level, stats, enemy type, etc.

Does the black version do ten times the damage? Are there any actual damage statistics available?

Both varieties of firebombs, black and regular, both inflict basic fire damage and do not scale with anything. The only difference is that black firebombs have a base damage of 250, which is 70 more damage than that of the normal firebomb at 180.