An accessory system for a vehicle includes a windshield that has a mounting element adhesively attached to its inner surface, an interior rearview mirror assembly, and an accessory support adapted for mounting to and demounting from the mounting element. The accessory support includes an accessory receiving portion configured to receive an accessory. The accessory support may comprise part of the interior rearview mirror assembly or may include a mirror mounting element with the interior rearview mirror assembly adapted for mounting to the mirror mounting element of the accessory support. The accessory comprises an imaging sensor and the accessory receiving portion is configured to receive the imaging sensor in a manner that compensates for the windshield angle of the windshield so that the imaging sensor has a more generally horizontal forward field of view through the windshield when the accessory support is mounted to the mounting element.