[danielf]

Believe it or not, fraudsters can actually detect when a tab has been left inactive for a while, and spy on your browser history to find out which websites you regularly visit, and therefore which pages to fake.

I might be wrong, but I'd imagine you'd have to have some malware running on you're computer in order for them to do that. I'd be surprised (well annoyed rather) if a site in one tab can read the browser history and change the url on another tab.