http://kb.mozillazine.org/Firewalls 

see http://kb.mozillazine.org/Firewalls Do a malware check with some malware scanning programs. 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/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 You can find the connection settings in Tools > Options > Advanced : Network : Connection If you do not need to use a proxy to connect to internet then select "No Proxy" if the default "Use the system proxy settings" setting doesn't work. See "Firefox connection settings": * https://support.mozilla.com/kb/Firefox+cannot+load+websites+but+other+programs+can