I am taking Continental airline from YYZ to HKG via EWR tomorrow. I would like to know if I need to buy duty free liquor, where should I buy it, at YYZ, EWR or in-flight?

I don't think I should buy at YYZ because then I may have trouble passing through EWR security. However I heard it is hard to find a duty free store in EWR. Anyone know where exactly it locates? Or should I buy it in flight, will it be more expensive?