Hi, Please check if this happens in [https://support.mozilla.com/en-US/kb/Safe%20Mode Safe Mode]. [http://kb.mozillazine.org/Problematic_extensions Problematic Extensions] [https://support.mozilla.com/en-US/kb/Troubleshooting%20extensions%20and%20themes Troubleshooting Extensions and Themes] [http://support.mozilla.com/en-US/kb/Uninstalling+add-ons Uninstalling Add-ons] [http://kb.mozillazine.org/Uninstalling_toolbars Uninstalling Toolbars] Safe mode disables the installed '''Extensions''', and themes ('''Appearance''') in '''Tools''' ('''Alt''' + '''T''') > '''Add-ons'''. Hardware acceleration is also temporarily disabled - the manual setting is '''Tools''' > '''Options''' > '''Advanced''' > '''General''' > '''Use hardware acceleration when available'''. [https://support.mozilla.org/en-US/kb/Options%20window%20-%20Advanced%20panel?as=u Options > Advanced]. All these settings/add-ons can also be individually or collectively disabled/enabled/changed in Firefox normal mode to check if an extension, theme or hardware acceleration is causing issues. [https://support.mozilla.org/en-US/kb/Options%20window Options]

That solved the problem, thanks! Turns out this was caused by a Skype Click to Call extension, which I never use anyway. I disabled it and the clipboard works fine. I was not able to remove the extension because there was no remove button on the extension listing--not that I could find, anyway.

You are welcome :) You can try to move to another location or delete the Skype add-on inside the '''e(E)xtensions''' folder in either the Firefox [http://kb.mozillazine.org/Installation_directory installation folder] or inside the '''Mozilla''' folder in '''%appdata%''' - type %appdata% in the Windows '''Run''' box (Windows key + '''R''').