Have you tried checking what is your home pages in Tools>Options>General? If not then go there and delete any webpages that you do not want as part of your home pages or reset to default. If you have done that then try clearing your cookies and cache, maybe that will work. You can clear cookies in Tools>Options>Privacy and clear the cache in Tools>Options>Advanced>Network. If neither of those work maybe changing the homepage in about:config will. It could also be a virus, try running a virus scan.

Adding to '''SandLizard''''s post: Check your add-ons for any suspicious extensions: * Tools (or [[Image: New Fx Menu]]) > Add-ons > Extensions Also check your list of install programs in Windows - Control Panel > Programs and Features. Usually malware comes bundled with other applications, so if you sort by date and see several applications installed at the same day, it may be easier to find suspicious applications that way. You can also check to see if your shortcut has been tampered with. Right click on your Firefox shortcut and select Properties. Check the target line under the Shortcut tab for any web pages after the "firefox.exe". You can try these free programs to scan for malware, which work with your existing antivirus software: * [http://www.malwarebytes.org/products/malwarebytes_free/ MalwareBytes' Anti-Malware] * [http://general-changelog-team.fr/en/downloads/viewdownload/20-outils-de-xplode/2-adwcleaner AdwCleaner] (for more info, see this [http://www.bleepingcomputer.com/download/adwcleaner/ alternate AdwCleaner download page]) * [http://www.microsoft.com/security/scanner/default.aspx Microsoft Safety Scanner] * [http://support.kaspersky.com/viruses/disinfection/5350 Anti-Rootkit Utility - TDSSKiller] * [http://www.surfright.nl/en/hitmanpro/ Hitman Pro] * [http://www.eset.com/us/online-scanner/ ESET Online Scanner] Further information can be found in the [[Troubleshoot Firefox issues caused by malware]] article. ------------------------- If you are suspecting your home page, you can try add-ons such as [https://addons.mozilla.org/en-US/firefox/addon/adblock-plus/ Adblock Plus] which can block advertisements on sites. If you are still having issues, did you download Firefox from the official Mozilla site? Sometimes if you search on Google or any search provider, they sometimes have "Advertised links" which are sometimes Firefox bundles that have been slightly modified. * https://www.mozilla.org/en-US/firefox/new/ If you did download from a different website and believe that to be the cause, you can report the link here: * https://www.mozilla.org/en-US/about/legal/fraud-report/