Boot the computer in Windows Safe Mode with network support (press F8 on the boot screen) as a test to see if this helps. Create a new profile as a test to check if your current profile is causing the problem. See "Creating a profile": *https://support.mozilla.org/kb/profile-manager-create-and-remove-firefox-profiles *http://kb.mozillazine.org/Standard_diagnostic_-_Firefox#Profile_issues If the new profile works then you can transfer some files from an existing profile to the new profile, but be cautious not to copy corrupted files to avoid carrying over the problem *http://kb.mozillazine.org/Transferring_data_to_a_new_profile_-_Firefox ----- Do a malware check with several 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