Generally speaking putting a capacitor across a pair of switch contacts is a very bad idea. Especially a large one. There are two reasons for this.

1) The capacitor dischage current is limited only by the resistance of the wiring. This can, over time, destroy the switch contacts.

2) If you very quickly discharge a large capacitor through a very low impedance you are likely to generate more noise at that instant than you filtered out since the last switch press.

If EMI in switch lines is an issue you should look first at clamping type components. Capacitors across switches should be a last resort and is used use as small of value as you possibly can and still ancieve the filtering you would desire.

Good Luck
Mike