Was playing arround with CSS. Especially with dynamic style settings like :hover. I  was naiv enough to use just a simple
<html><head> as a header for my experimental page. It made me wonder why Firefox 2 would not handle div:hover correctly, because Opera and Konquerer did. Finally changed the header to

<!DOCTYPE html PUBLIC “-//W3C//DTD XHMTL 1.0 Transitional//EN”
“http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd”> <html xmlns=”http://www.w3.org/1999/xhtml”>

… and now it works.