You're correct: FF is not a printable character. But I'm seeing the same issue with Firefox on Windows (with some monospace font). I suspect that the issue is w

You're correct: FF is not a printable character. But I'm seeing the same issue with Firefox on Windows (with some monospace font). I suspect that the issue is what Firefox complains about in the developer console: The file does not have a defined encoding. In fact, the Content-Type header is completely missing. I guess that those replacement glyphs are just Firefox playing it safe in the face of uncertainty regarding the character encoding.