Has it been set as a home page? See [[how to set the home page]] for details.

The unwanted web site is not as home page - I use the Google search page.

I just to confirm that you checked the home pages, Firefox can store multiple home pages. What is the site that keeps on appearing? If it is the Firefox has updated page, see [[Firefox has just updated tab shows each time you start Firefox]]. You can try running Firefox in [[safe mode|Firefox safe mode]] which will disable extensions and themes to test to see if one of them is causing the problem. If the site does not appear in safe mode, follow the procedure in the [[Troubleshooting extensions and themes]] article to identify the culprit. A possible cause of random pages loading is malware. If you suspect there is a chance that this is caused by malware, try running several malware scanners. It is best to run several as each will pick up things that the others miss. Some scanners you can try are: * [http://www.malwarebytes.org/mbam.php Malwarebytes] * [http://www.superantispyware.com/ SUPERAntiSpyware] * [http://www.lavasoft.com/products/ad_aware_free.php Ad-Aware] * [http://www.microsoft.com/windows/products/winfamily/defender/default.mspx Windows Defender] * [http://www.safer-networking.org/en/home/index.html Spybot S&D]