Older versions of Internet Explorer contain a defect in how <font> tags are handled. If your HTML output includes a <font> tag, and the specified font does not include the glyph, Internet Explorer changes the glyph to another that does occur in that font, and does a poor job of selection. Firefox simply ignores the <font> tag and shows the correct character, in compliance with the W3 specification.
By default, when you use CSS, DITA2Go does not include <font> tags in HTML output. However, you might need additional <font> tags in some circumstances. For example:
To turn on <font> tags in HTML output:
[HTMLOptions] ; NoFonts = Yes (default, prohibit <font ...> tags except for symbol ; fonts) or No (use <font...> tags, default if UseCSS=No) NoFonts = No
If you turn off CSS, DITA2Go turns on <font> tags by default; see §31.5 Understanding how CSS affects other options. If you do use CSS, you can create <span> tags instead, with a single setting for each character format; see §31.7.3 Mapping character formats to tags or span classes.
If you do not use CSS, and you are not using <font> tags either, you will get whatever fonts a browser specifies as defaults.