My start page problems were solved by rolling back Firefox 3 to Firefox 2. I installed Firefox 3 Release Candidate but it caused many troubles. Some of my favorite Firefox add-ons didn't work on Firefox 3. In addition, the Remember The Milk gadget for the Netvibes also didn't work on Firefox 3.

So, I uninstalled Firefox 3 RC version and installed Firefox 2 again. It seems OK now.