Oh, sorry to hear that it did not start in Firefox for you, I just tried it on my own install of firefox and it worked fine there.
Health pickups could be an option, yes, and it would work well. However, I think we wanted more of a challenging experience where the goal wasn't really to kill all enemies, but rather try to fight more one-on-one. The game could really do with quite a bit more polish, but we ran short on time.
I think we might have made a mistake with how punishing death is in the game, as you lose all your money. This makes it harder for the player to steadily progress.
There are many areas I feel where we could have improved it, and it was sorely in need of more playtesting :)