Annoying Home Page Opens Automatically

Whenever I restart my Mac, it automatically opens Mozilla and I am taken to this home page which I have never seen before:

http://sourceforge.net/projects/heat-meteo/

In my preferences I have set my Yahoo page but it does not default there; it opens the sourceforge url instead

Any suggestions on how to stop?

system preferences>accounts>your account>start up items tab>look here for something starting mozilla.