I too think that diversity helps: google has a monopoly in search, and a push for yahoo in search queries may even help them make the search engine better, and maybe they will become a much needed google competitor.
Mozilla and Google have been "frenemies" for a while. Now that Firefox is no longer supporting Google's search monopoly, I wonder how Google's search traffic (and stock price) will look in six months. I think Mozilla's decision is good for increasing search competition.
It will be same. Unless Yahoo have a real winning product (which given their track record, I doubt) people will just switch to google.
Does Yahoo still operate a search engine? I thought they used Bing.