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

See also:

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

Have you tried starting from Firefox in the Start Menu or the All Programs list. If it does, you can create a new desktop icon by dragging from the Start Menu(right click).

Hi Alan and cor-el, I have previously tried to launch Firefox from the start menu to no avail. I just clicked on the Firefox icon tonight, and it launched with no problem. I still have no idea why it has not been working for the past week??? Apparently there is no problem with security software as cor-el suggested as it launched tonight with no changes being made I'll keep using it as long as it works. Thanks for your help. Vic