I'm a little confused. Which .ini am I supposed to edit? Is it the mame.ini in the root ARCADE folder or the mame.ini in the ini folder? In the ini folder, I also see a plugin.ini. Do I have to change autofire to 1 and/or cheat to 1? When I enter a game, hit tab, click Plugin Options, I see Autofire. Under Add autofire button, I changed Input to P1 Button 1.
I've also checked that my P1 Button 1 is Kbd Z under Input. When I hold Z in the game, I still cannot perform autofire for some reason.
I think I solved my problem. I forgot that I also needed to bind a hotkey to the input. I think that autofire was different in the older ARCADE versions and that confused me. It also was not necessary to change cheat to 1.
It also looks like I didn't have to edit mame.ini. I just had to edit plugin.ini (changing autofire from 0 to 1) in the ini folder.
A weird problem I just found is that in plugin.ini, autofire keeps going back to 0 every time I close ARCADE. I have to keep editing plugin.ini because of this.