I just upgraded from Mozilla FireFox 0.8 to 0.9.2, for no other reason than because it was available. A sudden side-effect was that I could not login to Gmail anymore: I got an error 502. It still worked in IE, but FireFox is the browser I use for Gmail. I do unnecessary upgrading, I have multiple browsers, obviously I am not stopped by such a trivial error message.
But Passport is not perfect. And Yahoo has had vulnerabilities. As Bruce Schneier puts it: “Anyone can come up with a security system so clever that he can’t see its flaws.”