I have a MacBook Air, and recently purchased a second, to replace an old desktop. Now, on my MacBook a second firefox icon, with a gray square appears whenever my wife is using the new MacBook, even if Firefox is not running on her computer. If I click on the new icon, it takes me directly to whatever site she is browsing in Safari. Obviously something is being shared, but I've tried unsyncing different things, and it still happens. Is there any way to stop this? Attached is a screen shot. Thanks