Is that the Yahoo search page, Or a request to sign into yahoo using oauth to get your mail or calendar. I don't know anything about your setup, but prompts to sign into yahoo are generally the result of an attempt to authorize some function using oauth authentication and should be completed, not dismissed.

There is a "highjack malware" or something like that that whenever I open the ThunderBird E-Mail program I get redirected to a "Yahoo Search Page" and this page pops up 25 times in two minutes. I don't have to do anything other than open the ThunderBird E-Mail program.....then the Yahoo Search page starts popping up, OVER AND OVER AGAIN....sometimes as many as 25 times in a minute or two. Any idea why this happens? Thanks in advance.....