assign value to dropdown

how to assign value to dropdown in javascrip and it will wor mozilla also?

i used code like below but these are not worked in mozilla

document.getElementbyid('ddlname')options.value="352";

&

document.getElementbyid('ddlname')[document.getElementbyid('ddlname').selectedIndex].value="352";

&

document.getElementById('ddlName').selectedindex.value="352";