My website stylesheet sets the overall font size to be 76.1%, this was working fine except for Firefox and the pre tag, it would render fine in Internet Explorer but Firefox would shrink the font size down. In order to get around this I used the following CSS:

pre, code {
   font-size:  123.9%;
   *font-size: 100.0%;
}

The asterisk in front of the font-size command means it is strictly invalid CSS which is ignored by Firefox but is still parsed by Internet Explorer.