I have a Konica/Minolta Magicolor 2300DL attached to my home network. I print from Firefox 1.0 just fine.

Have you looked for updated network printer drivers from HP? It doesn't look from the site that there is anything more recent than Mar 2002. Are you using the PCL, or the Postscript drivers? I've found with HPs at work, that we have better luck with the PCL drivers.