Use Armor Protectant to make the door rubber sealant slippery so there is less chance to be frozen to door frame.
http://www.amazon.com/Clorox-Products-discoloring-temperatures-Water-based/dp/B004E2OBV4
Direction:
Spread Armor Protectant on the door rubber sealant, let it dry. Repeat it 5~6 times.
It does help in harsh winter.