Hi David.J.K., I'd try starting Firefox in [[Safe Mode]]. If you don't have the issue while all of your add-ons, extensions, and themes are disabled, you can try adding them back in one by one until you find the culprit. You should look at the [https://support.mozilla.org/en-US/kb/Troubleshooting-extensions-themes Extensions and Themes troubleshooting guide ] and the [[Troubleshooting plugins]] article as well. You should also read through [[Clipboard not working]] and http://kb.mozillazine.org/Clipboard_not_working article. Finally, your issue may be because you've been hit with some [https://support.mozilla.org/en-US/kb/Is%20my%20Firefox%20problem%20a%20result%20of%20malware?s=malware&r=0&e=sph&as=s#w_how-do-i-get-rid-of-malware Malware]. Hopefully this helps!