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.

See:

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

This is not the answetr to my problem both desktops have exactly the same settings for firewall and security and firefox works perfectly on my desktop but will not function at all on my wifes

Did you try to remove all the rules in the firewall for the Firefox program?

Try to boot the computer in Windows Safe mode with network support (press F8 on the boot screen) as a test to see if that helps.

The Reset Firefox feature can fix many issues by restoring Firefox to its factory default state while saving your essential information. Note: This will cause you to lose any Extensions, Open websites, and some Preferences.

To Reset Firefox do the following:

1. Go to Firefox > Help > Troubleshooting Information.
2. Click the "Reset Firefox" button.
3. Firefox will close and reset. After Firefox is done, it will show a window with the information that is imported. Click Finish.
4. Firefox will open with all factory defaults applied.

Further information can be found in the Refresh Firefox - reset add-ons and settings article.

There must be a significant difference between the two computers - I mean,next to Firefox working on one, but not the other one...

I use McAfee and Firefox has full unfettered access to the internet this setting is applied to both my desktop and my wifes and the program works perfectly on my desktop but will not work on hers

I have tried to reset firefox but when it opens at all it is imediatly frozen and the reset button will not work. I have uninstalled the program and reinstalled it and it still will not work

It is possible that the Firefox rules in security software are for an older (the previous) Firefox version and that the current Firefox version isn't allowed and blocked.
It is sometimes difficult to see that this is happening.

First the previous version of Firefox worked so there is nothing in its permissions that would possibly have been copied over that would stop the new version from working. Second THERE ARE NO FIREWALL PROGRAMS BLOCKING FIREFOXES ACCESS TO THE INTERNET! Third that would not cause the program to freeze and none of the buttons to work it would just keep webpages from loading. Firefox opens and imediatly freezes nothing works you cannot even get a drop down menu to from the firefox button so you cannot access the commands to reset firefox. Finally the program opens from the same folder on the hard drive and works perfectly on my desktop with the same security software and settings it just refuses to work on my wifes desktop on the same machine.