Yeah, I noticed that too about the browser version. An alternative fix is clicking the white part of the embedded html page next to the buttons or the buttons themselves. It was my first web port, so things are a bit messy, I'm sorry.
Oh, the dark level. You know that feeling when you play your game a lot and lose all feeling of what is acceptable difficulty and what's not? That's probably what happened here. I'll remove it, it's already too hard with a mouse, and with a light gun, you have no mouse pointer to show where you're shooting. It would just kill the Dreamcast version.
I'm really surprised you made it through all the way to the end. You can't be THAT evil. Thanks, man.