Hi steve.w.jones, the page that appears at startup is called the Home Page, and you can update that to a site you prefer: [[How to set the home page]] You can test using Command+n to launch a new window. If Firefox doesn't retain your preference between sessions, please check whether it's one of the issues discussed in this article: [[How to fix preferences that won't save]] If Command+n loads your preferred home page but you still get Yahoo at startup, I would consider that suspicious.

Thank you for your help