Oddly, I would actually say that IE is acting the most correctly in this situation.
Basically that technique of layout out form elements in the red box is a bit dodgy. Honestly, I think that's what tables are designed for (and it is tabular data):
<table id="zoek">
<tr>
<th>Land:</th>
<td><select>...</select></td>
</tr>
<tr>
<th>Plaats:</th>
<td><select>...</select></td>
</tr>
</table>
with:
#zoek th { font-weight: bold; text-align: left; }
#zoek td { text-align: right; }
Your CSS will be so much simpler (and I'm going to roll my eyes and shake my head in advance at any anti-table zealots in advance).
If you don't want to do that (for whatever reason), consider this as an arguably more robust technique:
<ul id="zoek">
<li><div class="label">Land:</div><div class="select"><select>...</select></li>
<li><div class="label">Price:</div><div class="select"><select>...</select></li>
</ul>
with:
#zoek li { overflow:hidden; }
#zoek div.label { float:left; }
#zoek div.select { float: right; }
Alternatively you can dispense with the list entirely and just nest some divs.