This is an indication that a firewall is blocking the new version of Firefox. For details see Firefox can't load websites but other browsers can.

A possible cause is security software (firewall) that blocks or restricts Firefox without informing you about that, 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.

See Server Not Found - Troubleshoot connection problems and Configure firewalls so that Firefox can access the Internet and http://kb.mozillazine.org/Firewalls

This was not a Firefox update, but a piece of malicious software you have inadvertently downloaded from a site called http://ffftp.co.cc/ which is impersonating Firefox. I discovered this as soon as my Zonealarm firewall requested permission for "Golds" to access the internet. Golds??!! However I couldn't find a file with this name installed on my computer.

You should delete the file you downloaded and do not allow internet access to any suspicious program. You should also scan your PC immediately for any virus, malware, etc. Best of luck.