I finally found something that dosen't wotk on FireFox: this web intranet interface I'm developing for this client simply do not work on Firefox. I'm not sure what the problem might be, but I asume it's badly formatted javascript - which unfortunally must remain like that since it's server-side generated. I also realized it's not possible to edit the propertie formname.elements[n].style on client-side with firefox (to make a textbox red, for instance).

I'll try to publish an example of this, and you'll be able to see for yourselves.