It makes sense for paste but It doesn't make sense for cut or copy.
Here's some text from Macromedia:
The System.setClipboard() method allows a SWF file to replace the contents of the Clipboard with a plain-text string of characters. This poses no security risk. To protect against the risk posed by passwords and other sensitive data being cut or copied to Clipboards, there is no corresponding "getClipboard" (read) method.
So as of today, you can use Flash to copy stuff to the clipboard anyway completing avoiding any security Mozilla/Firefox has anyway.
So we should simple allow at least copying.
It's disallowed for a reason: when I paste into a command prompt or IRC client, I shouldn't have to worry that some web site I have open might have put malicious code in my clipboard. If Flash allows that, I consider that a severe security hole in Flash.
-> wontfix / dup of bug 239481.
*** This bug has been marked as a duplicate of 239481 ***
I think I got the attention of some Macromedia people: