Let check a few things here:

What anti-virus do you have installed? is it F-Secure (It has been known to cause this problem before).

Have you tried to reset Firefox? Refresh Firefox - reset add-ons and settings

i'll try reseting ,, thanks lot

Which security software (firewall, anti-virus) do you have?

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

avast anti virus

thanks all it was from bit defender and the problem was solved successfully