Which encoding is selected when you see the hex code? *Firefox > Web Developer > Character Encoding *View > Character Encoding You can try to set the Boolean pref <b>gfx.font_rendering.directwrite.use_gdi_table_loading</b> to <i>false true</i> on the <b>about:config</b> page. *http://kb.mozillazine.org/about:config Can you post a link on a page where you see it? If you see such a box with hex code in it then that means that Firefox can't map a character to a specific font and you have to install a font that covers the affected characters.