We will demonstrate a behavior on the Paste button inside an editable text area.

If you right click on it, the Paste option is visible and Paste dialog is opened. You may need to change this default behavior and open dialog Paste as a plain text instead.

In this case can insert following line into the file: ~/CMSAdminControls/FCKeditor/editor/plugins/Shortcuts/fckplugin.js (or another registered script)

FCKCommands.LoadedCommands['Paste'] = new FCKPastePlainTextCommand();

Links to other resources: Custom FCK editor toolbar