Thanks all, my editor is back! I got the idea to go back into the Firefox configuration file and change the value of the network.enableIDN filter to true. I tried this before the update of moodlelib.php with no success, but this time it worked.
For anyone else with this issue, after installing the new php file open Firefox and type about:config in the address bar and press enter. Then in the Filter toolbar type network.enableIDN, then right click on the network.enableIDN item and select toggle to change the value to true. Restart Firefox.