What firefox version of it? and whether you have a real-time virus protection turned on?

My version of Mozilla is 30.0. I have a ESET NOD32 anti-virus software, which is always on.

ESET is one of the best software out there. So you can't get better than that IMO. Also, you're running XP which has reached EOL status and is no longer being supported by Microsoft so that's another security issue to worry about. I suggest upgrading to Windows 7 ASAP. Windows 8 is a let down. Or if you don't want to pay anything and be cheap like me, switch to Ubuntu. It's free, fast, and is currently on 14.10 with 14.04 LTS being supported for 5 years I believe. I don't remember. ---- But in case you want to keep Windoze, 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.<br> All these programs have free versions. 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 *AdwCleaner:<br>http://www.bleepingcomputer.com/download/adwcleaner/<br>http://www.softpedia.com/get/Antivirus/Removal-Tools/AdwCleaner.shtml *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. *Anti-rootkit utility TDSSKiller:<br>http://support.kaspersky.com/5350?el=88446 See also: *"Spyware on Windows": http://kb.mozillazine.org/Popups_not_blocked