To stop the enemy from firing in the classic arcade game in Galaga, destroy all the enemies but the two bee-like ships. Avoid their attacks for about fifteen minutes- they will stop firing. Once they have stopped firing for a significant amount of time, destroy them and for the rest of the game the enemy won't fire at you! (They will, however, still fly down at you. Gotta watch out for that.) This doesn't work on the newer games; they fixed the bug in a later version.