A vehicular interior rearview mirror system includes an interior rearview mirror assembly having one of (a) a variable reflectance reflective element and (b) a prismatic reflective element. The interior rearview mirror assembly includes a CMOS video microchip having, when the interior rearview mirror assembly is normally mounted in the vehicle, a field of view though the windshield forward of the vehicle and the interior rearview mirror assembly comprises electronic circuitry responsive to an input from the video microchip, the circuitry preferably controlling at least one headlamp of the vehicle. The mirror assembly may contain other accessories such as a compass sensor disposed in the mirror housing in the mirror housing behind and supported by the reflective element such that adjustment about at least one pivot joint by the driver to set the rearward field view of the reflective element moves the compass sensor in tandem with movement of the reflective element.