Firefox drop down error

I have a problem with a drop down in Firefox. It loads country flags from the database and works fine in all browsers except FF. In Firefox the drop down loads under other fields in the pages such as buttons and the search field. I attached a screenshot. AJAX is used and in the html we have the following code:

<a href="" class="dropDownSelect"  id="calCountryDropDown"
		onclick="showDropDown('calCountryDropDownList'); return false" onmouseout="delayHide('calCountryDropDownList');"><img src="/assets/images_new/flags/1.png" alt="Flag" class="flag" /><span></span></a>

	<ol id="calCountryDropDownList" class="dropDownList" onmouseout="delayHide(this.id);" onmouseover="clearHide();">
	Loading...[/CODE

[IMG]http://www.offerteselectie.nl/testofferte/ff-error.png[/IMG]


See how the image next to 'Add to calendar' lies on top of the drop down with flags.

Does anybody know what the problem is?

Code (markup):