A striker-fired firearm in one embodiment includes a firing mechanism having a spring-biased blocker movable into and out of the linear path traveled by the striker to reach a chambered cartridge. A sear operates to hold the striker in a cocked position. A blocker lifter actuated by a trigger mechanism via a trigger pull raises the blocker and actuates the sear to release the striker for discharging the firearm. Upon release of the trigger, the blocker automatically returns to a blocking position obstructing the linear travel path of the striker to disable the firing mechanism.