Hi,

If you have security software (ZoneAlarm??, other antivirus, firewall etc.) installed, you can try deleting all existing instances of Firefox and its related processes/files in all the different configuration modules/areas of the security software like process monitoring, sub/spawned process control, virtualization, HIPS etc., in addition to the security software's main configuration panel. Instead create new fully allowed/trusted rules for Firefox + its related processes in all the different modules/panels - a genuine/original Firefox installer as well as all the installed EXEs (Application) and DLLs (Application extension) are digitally signed by Mozilla Corporation (right-click > Properties > Digital Signatures). Even otherwise, some security software may also ask again when Firefox and/or its sub processes are started, and you may be able to allow/trust at that time. Please see this.

AV/Firewalls Configuration

You can also try to check in Windows Safe Mode with Networking.

Safe Mode

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

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