This article covers why you would not be able to access any web sites after upgrading Firefox. You may instead get "Unable to connect" or "Server not found" error pages.

• For situations unrelated to a Firefox upgrade, see Error loading web sites.

The most common cause of this problem is firewall software. Some firewalls silently block the updated version of Firefox from accessing to the Internet. Even if the firewall is supposedly disabled or uninstalled, it may still be active. You will have to configure these firewalls to allow Firefox access. Specific instructions for some firewalls are linked to below.

• AVG Internet Security
• BitDefender Internet Security
• CA Internet Security Suite
• Comodo Firewall Pro
• F-Secure Internet Security
• Kaspersky Internet Security
• Norton 360
• Norton Internet Security
• Online Armor Free
• Panda Internet Security
• Trend Micro Internet Security
• Windows Firewall
• ZoneAlarm