Multiple tabs with sites or just blanks ?
Chrome :
If they are redirecting sites then try :
1)uninstalling every suspicious programm (control panel or better revo uninstaller)
2)Go on chrome settings : settings > on startup >open specific or set of pages > delete everything
3)On settings : search > set google and delete everything else
4)Settings : Scroll down , go on advanced settings >select reset settings (if non of the previous works )
Firefox is similar