I’m checking my website right now with Firefox 5, and I see that the rendering of the fonts is terrible.
This is the difference between Firefox (5) and Chrome : just see for example the text Jeffe how is rendered…

The default font-family is :
font-family:"Times New Roman", Times, serif;
Why this behaviour? And how can I fix this trouble?
My actual OS : Windows 7 Professional
You can try using CSS Reset to reduce inconsistencies between different browsers.
Look up: https://stackoverflow.com/questions/116754/best-css-reset, or search online for
css reset.I can’t guarantee that this will work, but it should help. You can even customize it to get what you want.
(IMO, it’s not that horrible. I actually like the font better than chrome.)
Note:
Brad said (in your comments) that you should not depend on rendering fonts in a specific way. I agree with this. In addition, some people may like the font the way it is. It is much better to leave it alone, rather than trying to control the font rendering.