Yahoo search is gone. Now when you search something on a bookmarked Yahoo Search it will go straight to Twitter when using Firefox New Tab page.
That link is over three years old. As mentioned in posts 6 and 8, you can choose whatever search you want as default. I'm glad you were able to do that and get what you want."Firefox has kicked Google to the curb and run into the arms of Yahoo as its default search engine."
Not sure why mine defaults to Twitter.