Ive used the specially labled mirror sticky pads from Halfords on a few cars - never had one fall off after sticking the mirror on properly with the pad.
You need to make sure the screen and mirror are clean, smooth, and grease free. It helps if you use a hairdryer to heat the screen where your gonna stick the mirror and the mirror before attaching the double sided sticky pad.
Most recently I used this method on the Honda (With a Fiesta Mirror) and its still there - also remember, this car has very stiff suspension, and the car gets a lot of vibration....
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