Scrollable data table and header

[landho]

I have problem with displaying table header in scrollable data table when using Mozzila. In Internet Explorer headers are rendered perfectly but in Mozzila they are not visible at all. I saw that in richfaces live demo application headers are perfectly rendered both in IE and Mozzila,so this must be possible. Here is part of my xhtml that uses scrollableDataTable:

<rich:tabPanel switchType="client" height="250px" contentClass="dokument_stavke">
 <rich:tab name="tabGume" label="#{lab.GUMA_TITLE}">
 <rich:scrollableDataTable rowKeyVar="rkv" height="250px" width="100%" headerClass="headerTabStavke"
 id="listaGuma" rows="10"
 value="#{bean.stavkeGume}" var="lista">

 <rich:column id="sifra" sortable="false">
 <f:facet name="header">
 <h:outputText styleClass="headerText" value="#{lab.SIFARNIK_SIFRA}" />
 </f:facet>
 #{lista.gumaBean.sifra}
 </rich:column>

 </rich:scrollableDataTable>
 </rich:tab>
 </rich:tabPanel>