Is it possible to block this behavior at the browser level? Other than an addon: https://addons.mozilla.org/en-US/firefox/addon/re-enable-rig...
- open developer tools (CTRL-SHIFT-I, or F12)
- make sure you are on Elements tab
- click on '<body class=...' tag line
- then in the right hand panel switch to Event Listeners tab
- remove anything you like(contextmenu, cut, copy, paste in this case)
I'm sure there is a similar way in Firefox...