What exactly are you trying to copy? A text paragraph? How do you copy? Using right-click?

Could you share a screenshot?

It happens with any text on any page; cannot copy using right-click, nor using ctrl-c

Hm, it sounds like an extension prevents the use of the Copy/Paste feature. Did you try to disable all extension? Than restart Firefox. Are you able to copy and paste Text?

Do the alternatives not work as well?

• Copy: Ctrl+C or Ctrl+Insert (Mac: Command+C)
• Paste: Ctrl+V or Shift+Insert (Mac: Command+V)
• Cut: Ctrl+X or Shift+Delete (Mac: Command+X)

Did you try the Edit menu?

Start Firefox in Safe Mode to check if one of the extensions ("3-bar" menu button or Tools -> Add-ons -> Extensions) or if hardware acceleration is causing the problem.

• switch to the DEFAULT theme: "3-bar" menu button or Tools -> Add-ons -> Themes
• do NOT click the "Refresh Firefox" button on the Safe Mode start window

• https://support.mozilla.org/en-US/kb/troubleshoot-firefox-issues-using-safe-mode
• https://support.mozilla.org/en-US/kb/troubleshoot-extensions-themes-to-fix-problems

Boot the computer in Windows Safe Mode with network support to see if that has effect.

• https://www.bleepingcomputer.com/tutorials/how-to-start-windows-in-safe-mode/
• https://www.7tutorials.com/4-ways-boot-safe-mode-windows-10

I only have one add on/extension. UBlock. I am not sure how that could be causing the same issue of copy/paste that someone else is having.

Is the suggestion to disable this extension and then see if copy/paste works?

Did you try Safe Mode?

If it works in Safe Mode and in normal mode with all extensions ("3-bar" menu button or Tools -> Add-ons -> Extensions) disabled then try to find which extension is causing the problem by enabling one extension at a time until the problem reappears.

• https://support.mozilla.org/en-US/kb/troubleshoot-extensions-themes-to-fix-problems

Close and restart Firefox after each change via one of these:

• "3-bar" menu button -> Exit (Power button)
• Windows: File -> Exit
• Mac: Firefox -> Quit Firefox
• Linux: File -> Quit

Do a clean reinstall of the current Firefox release and delete the Firefox program folder before installing a fresh copy of the current Firefox release.

• download the Firefox installer and save the file to the desktop
  *https://www.mozilla.org/en-US/firefox/all/

If possible uninstall your current Firefox version to cleanup the Windows Registry and settings in security software.

• do NOT remove "personal data" when you uninstall the current Firefox version, because this will remove all profile folders and you lose personal data like bookmarks and passwords including personal data in profiles created by other Firefox versions

Remove the Firefox program folder before installing that newly downloaded copy of the Firefox installer.

• (64-bit Firefox) "C:\Program Files\Mozilla Firefox\"
• (32-bit Firefox) "C:\Program Files (x86)\Mozilla Firefox\"

• it is important to delete the Firefox program folder to remove all the files and make sure there are no problems with files that were leftover after uninstalling
• http://kb.mozillazine.org/Uninstalling_Firefox

Your personal data like bookmarks is stored in the Firefox profile folder, so you won't lose personal data when you reinstall or update Firefox, but make sure NOT to remove personal data when you uninstall Firefox as that will remove all Firefox profile folders and you lose your personal data.

• https://support.mozilla.org/en-US/kb/Profiles
• https://support.mozilla.org/en-US/kb/back-and-restore-information-firefox-profiles

Reinstall Firefox

• https://support.mozilla.org/en-US/kb/troubleshoot-and-diagnose-firefox-problems

Firefox will not allow you to right click copy and then paste, copy/paste, copy & paste.

Have experienced this issue ongoing for approx 2 years and found it is solved only when you allow the new Firefox version to be deployed.

Firefox passively aggressively forces you to upgrade to their new version by removing your most basic browser feature to right click copy/paste if you do not accept their upgrade after approx. 2 weeks.

If you click "not now" multiple time to accept the Firefox browser upgrade Firefox will eventually eliminate your ability to right click copy/paste until you accept their new version.

In the meantime, you can only highlight copy and then paste by using keyboard "Ctrl V".

PS ............. I just had this issue again today after clicking "not now" for the past 2 weeks .............. Firefox then blocked my ability to copy/paste and it has now been solved after accepting their new version.

This may not be your same issue but it is mine and it is very frustrating to not be able to use a basic browser feature if you do not accept their upgrade.