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Being a Glock, it will NOT fire when dropped, unless something's broken (or as previously mentioned, if someone tried to grab it and got their finger in the trigger guard).

Glocks have not just the little doohickey on the trigger, but a firing pin block as well. The firing pin has a cutout on one side that matches a vertical plunger held inside the slide. When the trigger is depressed, a portion of the trigger mechanism pushes this spring-loaded plunger up, freeing the firing pin. Until the trigger is pulled, that firing pin -cannot- reach the primer of the chambered round.

AR 15s, most pump shotguns, and several other firearms lack this mechanism, and are not safe to drop with a loaded chamber. Glocks, however, along with most modern pistols, are perfectly safe when dropped. It's still unnerving to have the wrong end of it pointed at one's self, though.