Is there a setting in Firefox to display a pop-up ad when clicking a form field? I can't imagine... I suspect a rogue add-on. Could you review your extensions on the following tab and disable ALL nonessential and unrecognized extensions. Then restart Firefox and test. orange Firefox button (or Tools menu) > Add-ons > Extensions category Any change?

Do a malware check with some malware scanning programs on the Windows computer.<br /> Please 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