function does not work with Netscape, works OK with IE, Mozi

[admin]

I have a script that works fine with IE 6.0 and Mozilla, but not with my Netscape 4.49.
Can anyone give me a clue here?

I get error message in Netscape:

document.forms[0].Month has no properties.

Here is script:

<SCRIPT Language='JavaScript'>

function ShowMap() {
Month = document.forms[0].Month.options[document.forms [0].Month.selectedIndex].value;
Day = document.forms[0].Day.options[document.forms[0].Day.selectedIndex].text;
Year = document.forms[0].Year.options[document.forms[0].Year.selectedIndex].text;

document.open('http://docs.lib.noaa.gov/rescue/dwm/' + Year + '/' + Year + Month + Day + '.djvu','_blank','','false');


}