When copying some content on a web page, it can happen that the clipboard contains more than what is visibly selected.

This is done for

In the 25C3 talk "Tricks: makes you smile" (demo), it was called WYSINWYC (What you see is not what you copy).

I’m looking for a Firefox solution (preferably an add-on), which must be FLOSS, that can notify/warn me somehow as soon as I have copied something invisible.
Because the hidden text can be injected via JavaScript, the warning should happen after copying (i.e., the content is in the clipboard), not after selecting.

(Some time ago, I suggested to include this in NoScript, but it’s probably not going to happen.)


1 Answer 1


In firefox urlbar:

type in about:config and press enter.

Then try this: type in dom.event.clipboardevents.enabled in the bar below the url bar, and set to false by double clicking on the true.

This should disable clipboard manipulation.

  • 1
    And what does this downvote mean? The person doesn't like me, the solution doesn't work, or because it isn't a plugin (which the OP said it didn't have to be). The plugin that did just what OP wanted stated the above same thing. Commented Aug 28, 2014 at 21:33
  • 1
    Not my down vote, but maybe because it’s only a partial solution, as it a) doesn’t work for non-JS (i.e., CSS) implementations, and b) doesn’t warn/notify but completely prevents (which is not necessarily a bad thing; depends on the case). So, it’s not a matching solution, but certainly better than having nothing -- thanks for the tip!
    – unor
    Commented Aug 29, 2014 at 8:08
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    It will probably be impossible to prevent the 'CSS' method as it's almost impossible to detect what's needed and what isn't by automated means. Commented Aug 30, 2014 at 18:06

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