Hi,

Please check if this happens in Safe Mode.

Problematic Extensions

Troubleshooting Extensions and Themes

Uninstalling Add-ons

Uninstalling Toolbars

Also do a malware check with some malware scanning programs on the Windows computer.
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/security/scanner/en-us/default.aspx - Microsoft Safety Scanner
• 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

Thanks for your ideas - I tried them all but the problem is still there. I have also scanned my system for malware etc and it comes up with a clean report on webroot and AVG

One thing I did notice is that the problem is in all the search engines on the tool bar so includes yahoo and bing

Looks like I need a different browser if I need to use search. Perhaps the problem will sort itself out on a future Firefox upgrade?

The AVG Safe Search is known to cause such problems. Please see this.