select onchange option how to make it work on netscape

[admin]

I got a big problem I got a function that need to work on onchange
<SELECT name="FirstSelectMonth" onchange="ChangeOptionDays('FirstSelect');">
<OPTION>Jan
<OPTION>Fev
<OPTION>Mar
<OPTION>Avr
<OPTION>Mai
<OPTION>Jun
<OPTION>Jui
<OPTION>Aou
<OPTION>Sep
<OPTION>Oct
<OPTION>Nov
<OPTION>Dec
</SELECT>
on explorer it work but not on netscape how can I fix that
thanks