Google's account system is global, single sign-on. That sounds like a good idea but it's not. It means I can't be signed into GMail in my Firefox window without Google mangling my search results pages at the same time in another tab. What happens is that Google activates some kind of javascript onclick handlers so that I can't Ctrl-Click for tabbed browsing through search results anymore. Intensely annoying. Yahoo, thankfully, doesn't do this (I'm not logged in to Yahoo) so now I have to switch search engines.
Now I've posted about it here, and contacted Google Accounts about it. Let's see if anyone responds.

[UPDATE: I'm not perfectly sure that this isn't somehow also horrible breakage in Firefox, but still Yahoo doesn't give me this problem]