See this - https://support.mozilla.org/en-US/kb/troubleshoot-firefox-issues-caused-malware

Is this only happening when you open a new tab? You can check the browser.newtab.url pref(s) on the <b>about:config</b> page. *http://kb.mozillazine.org/about:config *https://support.mozilla.org/kb/new-tab-page-show-hide-and-customize-top-sites You can use the SearchReset extension to reset some preferences to the default values. *https://addons.mozilla.org/firefox/addon/searchreset/ Note that the SearchReset extension only runs once and then uninstalls automatically, so it won't show on the "Firefox > Add-ons" page (about:addons).

You can try these free programs to scan for malware, which work with your existing antivirus software: * [http://www.microsoft.com/security/scanner/default.aspx Microsoft Safety Scanner] * [http://www.malwarebytes.org/products/malwarebytes_free/ MalwareBytes' Anti-Malware] * [http://support.kaspersky.com/faq/?qid=208283363 TDSSKiller - AntiRootkit Utility] * [http://www.surfright.nl/en/hitmanpro/ Hitman Pro] * [http://www.eset.com/us/online-scanner/ ESET Online Scanner] [http://windows.microsoft.com/MSE Microsoft Security Essentials] is a good permanent antivirus for Windows 7/Vista/XP if you don't already have one. Further information can be found in the [[Troubleshoot Firefox issues caused by malware]] article. Did this fix your problems? Please report back to us!