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 and the updater process.

See:

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

Put McAfee back to default, no luck. Then just to see if it was anything to do with the firewall I turned it off and still was unable to connect with Firefox so its not the firewall. Any further suggestions as to what could have changed on the upgrade?

I also receive the following notice :, The operation can not be completed because of an internal failure. A secure network communication has not been cleaned up correctly. Not sure why this come up or whether its on opening or closeing the FF , this is the second time it has come up. Possibly because I am trying to restart FF before it has time to close out fully?

Also now when I try to use FF it tells me I have it running and need to first close it.