A possible cause is security software (firewall,anti-virus) 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 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.

Also try uninstalling and the re-installing any Security program.

See:

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

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

Did all of that and reset fectory settings on laptop to no avail.

This has never happened before the latest update

Some problems occurs when your Internet security program was set to trust the previous version of Firefox, but no longer recognizes your updated version as trusted. Now how to fix the problem: To allow Firefox to connect to the Internet again:

• Make sure your Internet security software is up-to-date (i.e. you are running the latest version)
  
  
• Remove Firefox from your program's list of trusted or recognized programs, then add it back. For detailed instructions, see Configure firewalls so that Firefox can access the Internet.