Some software firewalls have a program control feature that will disable access if the program files are changed. This typically appears after an update. However, I don't know whether this applies to your firewall. Could you provide a little more information about it?

Remove all rules for Firefox and the plugin-container 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 and the updater process.

See:

• https://support.mozilla.org/kb/Server+not+found
• https://support.mozilla.org/kb/Firewalls