PayPal And Ice Dragon?

I was buying something online from a site I have used many times. Everything went well until I came to the PayPal link at the checkout when it wouldn’t accept my info email & password (gave me the wrong info message even though I knew it was correct). After a couple of unsuccessful attempts to resolve this I then signed out of Ice Dragon and opened the Firefox browser instead and the deal went through without a hitch. Any explanation of why I couldn’t complete the payment via Ice Dragon?.