What he means is that the webpages are not served as utf8, so characters outside the us-ascii (what firefox tell me this page is encoded in) will not get through to fossil when sending post information with utf8 characters.

also, it seems these pages are served with this http header:

  Content-type: text/html; charset=ANSI_X3.4-1968

setting charset to utf8 might help (or adding meta tag)