To play:

• The keys: Ctrl = left flipper; Alt = right flipper; Space = shooter (the thing that puts the ball into play)
• To have more than 1 player, hold down Ctrl and tap Alt until you have 2,3,4 players (PL2,PL3,PL4) (MAME shows bd instead of PL)
• The default speed is 2. To change, Hold down Alt and tap Ctrl to change (SP1 or SP3) (MAME shows Sb instead of SP)
• Press Space to start. Display will show (player - ball) (MAME shows 1F1 instead of 1-1)
• Press Space to get the ball into play. Display will show your score. Now you are playing.

Here is the Parker Brothers Wildfire Manual.