Store in a cool dry place and refrigerate after opening. Proper fridge storage: Store perishables (basically anything without vinegar or spice) in the center of the fridge/main portion and NOT the door. The main portion of the fridge is a consistent temperature, which is the goal. The door changes temperature degrees, sometimes drastically, depending on how often the fridge is opened, how long it stays open, etc.
Marmalades last closer to six months in the fridge with the risk of crystallizing (this doesn't mean they are bad, just difficult to use. Suggest putting the jar in the pot of boiling water for 5-10 minutes. This usually helps liquefy).
If not using immediately, store in a cool, dry place for up to a year for maximum freshness unopened. The shelf life for marmalades is about 2 years.