hello, maybe you are in fullscreen mode - try to press f11 in order to switch it off...

In case the problem is an update to Firefox or to an add-on, could you also try starting Firefox in its Safe Mode? Hold down the Shift key when starting Firefox. Then in the small dialog that should appear, choose "Start in Safe Mode". Any difference?

To exit Firefox when there are no visible controls, try using Alt+F4, which is a global Windows shortcut to "close this window" or Ctrl+w which in Firefox will close the current tab. (If you have clicked a Flash player or other plugin in the page, these shortcuts might be intercepted by the plugin instead.)

It is possible that your security software (firewall, anti-virus) 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

• https://support.mozilla.org/kb/fix-problems-connecting-websites-after-updating

Thank you - hitting F11 to get out of full screen mode worked perfectly!  :)