A breakaway mounting assembly supports a rearview mirror or other accessory on an improved windshield mounted button. The mounting assembly includes a base having a mount for the accessory or mirror, and a plurality of resilient flanges which engage, hold, and center the assembly on the button but flex to release the assembly if impacted from virtually any direction. Preferably, the resilient flanges are formed in one piece with a retainer mounted on the base by a plurality of mounting flanges also formed in one piece with the retainer and engaging a shoulder on the base. An open release space is defined between a pair of the flanges, while the base has an unobstructed open area aligned with the release space through which the button may be released when the mirror or accessory is impacted directly from the mirror reflecting surface. An inclined wall surface on the base cams the assembly off the button when the mirror or accessory is impacted from the side. The button is tapered toward a curved top end and the windshield attachment surface and has a recess at its bottom end adapted to receive one of the resilient flanges.