I noticed something like that with IE years ago. That's why I'm always careful about cookies, etc on my main user account. I don't even log in anymore to my accounts with my main user. I just switch over to my protected users and it's been fine.
One user for one eBay and PayPal account and it's easy.
You gotta be web based Modee... Gmail is king of emails, use a flash drive to transfer files over to another user, keep track of everything in a notepad or an excel file. It's golden.
But you're quite skilled in all this so it's okay for you, but for everyone else I recommend using user accounts. The main reason for it is flash objects, which when disturbed sometimes cause limitations on your accounts. User accounts keeps flash objects in tact, keeping eBay and PayPal happy.