I finally found one of the main problems.
My Konqueror by default uses "URW Palladio L" as font, and I didn't translate this into the CSS (where I had a typo which kept teh font-family tag from being used). Firefox instead uses a font which just doesn't look as well at the given size.
So I now changed the font to "URW Palladio L". Could you please check, if it is avaible for your platform?
Mostly this means: Could you test the font on firefox in Windows?
Phex - take back p2p