Please update to Firefox 18.0.1 [[Update Firefox to the latest version]] Then Reset Firefox [[Reset Firefox – easily fix most problems]] Also scan for malware [[Troubleshoot Firefox issues caused by malware]]

Thanks for your response but unfortunately these steps do not solve the problem - other ideas?

You ran full malware scans with all the programs? That was fast

Do a malware check with some malware scanning programs on the Windows computer.<br /> 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. *Malwarebytes' Anti-Malware:<br>http://www.malwarebytes.org/mbam.php *SuperAntispyware:<br>http://www.superantispyware.com/ *Microsoft Safety Scanner:<br>http://www.microsoft.com/security/scanner/en-us/default.aspx *Windows Defender: Home Page:<br>http://www.microsoft.com/windows/products/winfamily/defender/default.mspx *Spybot Search & Destroy:<br>http://www.safer-networking.org/en/index.html *Kasperky Free Security Scan:<br>http://www.kaspersky.com/security-scan You can also do a check for a rootkit infection with TDSSKiller. *http://support.kaspersky.com/viruses/solutions?qid=208280684 See also: *"Spyware on Windows": http://kb.mozillazine.org/Popups_not_blocked