Yesterday, Sam pinged me with a screenshot of Yahoo's explicit endorsement of Firefox 3.
The link takes you to http://downloads.yahoo.com/firefox/ which only seems to work on IE at this time (if you use FF to access that page, it will ask you to download the Yahoo toolbar instead).
Ironically, the same day that users spotted this Firefox 3 endorsement, Internet Explorer 8 Beta 2 was released. On the IEBlog, users can see the new features available to them in the newest version of Internet Explorer. On a similar note, Danny Sullivan reviewed IE8 with how it relates to search functionality.