The 2 browser method is used to apply for 2 identical cards at the same time. The cookies are key to your specific bonus so if you were to apply for 2 cards, one through IE and one through Firefox, you would be able to get instant approval for both (assuming you qualify). Normally, credit card companies don't allow you to have more than one of the same product so the 2 browser method is a way to get around it by submitting 2 apps at once each with unique identifiers