I'm responding here because this is where you first asked about this, and it should be separate. In the other thread where you mentioned it though, I see you were using a loader function to initiate this script. That's fine, you can do that. But if you do, you should not load it a second time using the body onload attribute.
Now, once you've got that settled, the problem with opening the selection in the same window is that the form submits before that happens. To prevent that, add the highlighted to the HTML portion of the code:
Code:
<form name="listmenu0" class="form" onsubmit="return false;">
<div class="row">
<select class="c-input size-2" name="firstlevel"></select>
<select class="c-input size-2" name="secondlevel"></select>
<select class="c-input size-2" na . . .
Bookmarks