This article covers why you would not be able to access any websites 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 cause

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.

To fix it

1. Make sure your firewall is up-to-date.
2. If updating the firewall doesn't correct the problem, remove the Firefox entries and add them again.

Below are links to tutorials on configuring certain firewalls. Click on the tutorial for the firewall you are using.

• AVG Internet Security
• Avira Premium Security Suite (Avira Knowledge Base)
• BitDefender Internet Security
• CA Internet Security Suite
• Comodo Internet Security
• Comodo Firewall Pro
• F-Secure Internet Security
• Kaspersky Internet Security
• McAfee Internet Security
• Norton 360
• Norton Internet Security
• Online Armor Free
• Panda Internet Security
• Trend Micro Internet Security
• Windows Firewall
• ZoneAlarm Free Firewall

Find out which Firewalls are installed (Windows only)

Enum Process is an application that detects firewall processes and services. See this page for more information. This tool is not created by Mozilla.

1. Download Enum Process.
2. After downloading, double-click EnumProcess.exe.
3. Select Run.
4. In the drop-down menu to the right, select Simple.
   
   
   
5. Click List Processes.
   
   
   

If you see the message "No known processes detected", that means no firewalls were found. You should then remove the Enum Process program from your computer as you won't have anymore use for it.