To protect users' private information, unprivileged scripts cannot invoke the Cut, Copy, and Paste commands in the Mozilla rich text editor, so the corresponding buttons on the Mozilla Rich Text Editing demo page will not work. To enable these functions, you must modify your browser preferences.

   Quit Firefox. If you have Quick Launch running (on Windows, this is an icon in the toolbar), quit that too.
   Find your Firefox profile directory.
   Open the prefs.js  file from that directory in a text editor. If there's no prefs.js file, create one.
   Add these lines to the prefs.js file:

   user_pref("capability.policy.policynames", "allowclipboard");
   user_pref("capability.policy.allowclipboard.sites", "https://www.mozilla.org");
   user_pref("capability.policy.allowclipboard.Clipboard.cutcopy", "allAccess");
   user_pref("capability.policy.allowclipboard.Clipboard.paste", "allAccess");

   Change the url https://www.mozilla.org to the site for which you want to enable this function.
   Save the file and restart Firefox. The Clipboard buttons should now function.

Hell Sir : i am using a host manager ( GVO company ) , http://www.gogvo.com/ which is hostthen profit , when i try to create a message , when i tried to use copy & paste options , i got this message : Copy/Cut/Paste is not available in Mozilla and Firefox. Do you want more information about this issue? SO , i clicked on " OK " to know more information about this issue , i find that as explained , i have to modify my browser preferences. & open the prefs.js file from that directory .BUT ... the problem that i can not open this " prefs.js" file ????! THE MESSAGE IS HERE BELOW , PLS READ : To protect users' private information, unprivileged scripts cannot invoke the Cut, Copy, and Paste commands in the Mozilla rich text editor, so the corresponding buttons on the Mozilla Rich Text Editing demo page will not work. To enable these functions, you must modify your browser preferences. Note: In the newer versions of Firefox, the preferences filename has changed from user.js to prefs.js. Changing the preferences in Firefox Quit Firefox. If you have Quick Launch running (on Windows, this is an icon in the toolbar), quit that too. Find your Firefox profile directory. Open the prefs.js file from that directory in a text editor. If there's no prefs.js file, create one. Add these lines to the prefs.js file: user_pref("capability.policy.policynames", "allowclipboard"); user_pref("capability.policy.allowclipboard.sites", "https://www.mozilla.org"); user_pref("capability.policy.allowclipboard.Clipboard.cutcopy", "allAccess"); user_pref("capability.policy.allowclipboard.Clipboard.paste", "allAccess"); Change the url https://www.mozilla.org to the site for which you want to enable this function. Save the file and restart Firefox. The Clipboard buttons should now function.