Here is a link to an add-on from Firefox. It should allow you to copy & paste. After I installed it, I logged into Moodle and went to where I was experiencing the script error. In the bottom left corner of the dialog box where I was typing there was a little message in red telling me that copying and pasting was not available. When I clicked on the message it allowed me to add my moodle site to a list that would allow copying and pasting.
Here is the link: https://addons.mozilla.org/en-US/firefox/addon/allowclipboard-helper/.