Hi! go to Firefox -> Preferences. Once you are able to open a small window with a lot of options read on.

The first section under General tab will have your home page settings. There you can set what you want to see when you start Firefox. For the option - 'When Firefox starts' select 'Show my homepage' from the drop down menu. In the next line you should enter www.google.com as your home page.

These settings might have been changed by some malicious script. If this does not help and the problem persists you should run a virus scan and re post this problem under security threats or a similar thread.

Do a malware check with some malware scanning programs.
You need to scan with all programs because each program detects different malware.
Make sure that you update each program to get the latest version of their databases before doing a scan.

• http://www.malwarebytes.org/mbam.php - Malwarebytes' Anti-Malware
• http://www.superantispyware.com/ - SuperAntispyware
• http://www.microsoft.com/windows/products/winfamily/defender/default.mspx - Windows Defender: Home Page
• http://www.safer-networking.org/en/index.html - Spybot Search & Destroy
• http://www.lavasoft.com/products/ad_aware_free.php - Ad-Aware Free

See also:

• "Spyware on Windows": http://kb.mozillazine.org/Popups_not_blocked