@Yvonne - it can be a temporary failure of a local yahoo server eg. with mail at yahoo.tr (I say that because Your friends seem to have a similar problem). Yahoo must mend that we can only help with browser specific info for yahoo.mail
Today I have no problems at yahoo.com (except that it would not deliver 1 mail to the US - it contained a political comment / yahoo apparently does not like such comments
greetings to TR and AT from guenter in DE (Germany)
p. s. @vreak: es gibt manchmal Probleme die Yahoo mit Gecko Browsern wie K-Meleon verursacht / da versuchen wir zu helfen - deshalb sind wir für Yahoo.mail.probleme in der Suchmaschine