Yahoo and Firefox

[chickenfeet]

Does anyone know why/how Yahoo is hijacking web pages when viewing in Firefox.  It doesn't happen with other browsers and it only happens on some sites but it does include some major ones like The Guardian.  I'll be happily reading when suddenly I'm yanked away to something like

https://ca.search.yahoo.com/yhs/errorhandler?hspart=gt&hsimp=yhse-gt&q=http%3A%2F%2Ft.zemanta.com%2Fpageview%2F%3Fpost_id%3D33822&type=216107