Note: While he may be explaining it as pasting to word or email, the same applies when the pasting is done to another website.
According to your link, everything should be hunky-dory, because FR pages use UTF-8 encoding.
But what is happening is that the FR server is now converting incoming UTF-8 to garbage by replacing the individual bytes of each multi-byte UTF-8 group with the corresponding HTML entity. Thus, for example, the UTF-8 for the left double curly quote, e2 80 9c, gets replaced by three entities, circumflex-a, the Euro sign, and the oe ligature. As a result, the browser, even though it is correctly in UTF-8 mode, doesn't see the pristine UTF-8 character, but instead the three bogus characters.