Insert Coin: 5
Start Game (P1): 1
Btn 1: Left Ctrl
Btn 2: Alt
Btn 3: Space
Up, Down, Left, Right: Arrow / Cursor keys
Enter Full Screen: Alt + Enter (Firefox only)
Exit Full Screen: Esc
If game is stuck: Refesh page

To redefine keys within MAME (or to simply look at the current controls) simply press the Tab key.