Microsoft used its might inside the government to break apart those two willing partners
... one year later, Yahoo! is headed by a former Microsoft ally (Autodesk CEO) and a poisoned board of directors.
in contrast to Yahoo!'s recommendation of Firefox 3.0 last year (under Jerry Yang's leadership), Yahoo! now promotes IE8. Yahoo, and Amazon have decided to join together in the soon to be formed Open Book Alliance. Microsoft supported more aggressive actions, including lawsuits, against Google's book scanning [after giving up their own failed book scanning effort].
So Yahoo has joined the likes of Citrix, Corel and Novell and become a M$ vassal. Good bye, Yahoo, it was fun while it lasted. How sad it will be sad to see you look like Hotmail."