Re: How do I make Mozilla Firefox 3.6.13 my homepage (default page)?
See our knowledge base article How to set the home page to learn how you can set the home page to your liking (including restoring it to the default page).
Unrelated to your issue, it looks like you're using a very old version of Firefox. You should upgrade to the latest version -- just go to the Help menu and click Check for Updates. This link walks you through the process: Update Firefox to the latest version