A possible cause is security software (firewall) that blocks or restricts Firefox or the plugin-container process without informing you, possibly after detecting changes (update) to the Firefox program.

Remove all rules for Firefox from the permissions list in the firewall and let your firewall ask again for permission to get full unrestricted access to internet for Firefox and the plugin-container process.

See:

• Server Not Found - Troubleshoot connection problems
• Configure firewalls so that Firefox can access the Internet

These suggestions do not work. Any other ideas how I can use this wonderous new Firefox 4?

I gave up on Firefox 4 for a couple of months. I've just now tried again, and I have the same problem. It is not a firewall problem. I thought by now Firefox updates would have caught whatever is the problem. Perhaps someone in the forum community can offer alternate suggestions. I see that 10 people have reported this same problem.

• http://kb.mozillazine.org/Error_loading_websites
• http://kb.mozillazine.org/Browser_will_not_start_up