The newest version of Firefox has much to offer users. A cleaner interface, more intuitive browsing, and a shiny information disclosure vulnerability. The problem is that Firefox keeps a list of all recently closed tabs for users to refer to later if they accidentally close a tab. Malicious users can use scripts to pull this information from victim's browsers, allowing their recently viewed pages to be disclosed. And while this isn't as bad as most exploits are, you can imagine that this is a problem for anonymity. I recommend using Firefox with the x(Paranoid) addon which allows you to clear ALL private data including recently closed tabs.