Variable not defined in FireFox

I'm having a variable issue which appears in firefox (it works fine in IE)

Here is my code:

<form id="thePropertiesForm" name="thePropertiesForm" action="page-preview-properties.cfm" method="post">
	<input name="frmAdminPIPID" type="hidden" value="1"/>
	<input name="frmSectionID" type="hidden" value="1" />
	<input name="frmTask" type="hidden" value="1" />
</form>

function proceedToProperties(vStructureID) {

thePropertiesForm.frmAdminPIPID.value=vStructureID;
thePropertiesForm.frmSectionID.value=document.formPreview.sectionID.value;
thePropertiesForm.submit();

}

Code (markup):

In firefox I get there error thePropertiesForm is not defined.

Can anybody spot where I'm going wrong?

Thanks

 

Hi,
what if you insert document. before thePropertiesForm....?? Any better??

 

Brilliant, yes that worked

Many thanks