I cannot completely Clear Recent History; one url keeps showing up even after clearing. Why?

When I click on the Clear Recent History button, it appears that all categories are cleared. However, when I log back on, the drop-down menu of the URL bar shows that one previous URL from October 3, 2011, has not been cleared--has never been cleared, in fact. It is always the same address, which is: us.mc393.mail.yahoo.com/mc/welcome?gx=/&.tm=1317702807&.rand=42rlbj6nchdgv#_pg=showMessage&sMid=3&&filterBy=&.rand=248392308&midIndex=38... It is the only item to appear in the drop-down menu. Why is this happening, and how do I clear the history completely? Thank you. mjlink@yahoo.com