Are you using KDE or GNOME (or something else) as your Desktop Environment? If KDE, go to the KDE Control Center (not the Mandrake Control Center) and choose Appearances and Styles (or something like that) and change the font settings to something more useable (this will change all application/desktop/menu fonts, but the default choices already selected often cause problems like this). The effect on Mozilla may be limited, as Mozilla is somewhat better integrated with the GNOME desktop than with the KDE desktop (where you are expected to use Konqueror rather than Mozilla), but it does have an effect.
If you're using GNOME, go to the GNOME Control Center and choose Desktop Preferences=>Fonts and adjust the font settings to something more useable (the default font selection for GNOME is often as badly-behaved as the default font selection for KDE).
In both cases, a font such as the Bitstream Vera (sans, serif and sans mono) set, or the Luxi (sans, serif and mono) set often give better results than the default "serif", "sans-serif" and "monospace" choices. And of course if you have Windows fonts installed, Arial (sans serif), Times New Roman (serif) and Courier New (monospace) are always good choices.
Hope this helps.