FF3/Windows CSS z-index problem with YouTube player

Try to add the wmode parameter to be opaque like this:

(Note that it’s included in both a <param> tag and a wmode attribute on the <embed> tag.)

<object width="425" height="344"> 
    <param name="movie" value="http://www.youtube.com/v/Wj_JNwNbETA&hl=en&fs=1"> 
    <param name="type" value="application/x-shockwave-flash"> 
    <param name="allowfullscreen" value="true"> 
    <param name="allowscriptaccess" value="always"> 
    <param name="wmode" value="opaque" />
    <embed width="425" height="344"
            src="http://www.youtube.com/v/Wj_JNwNbETA&hl=en&fs=1"
            type="application/x-shockwave-flash"
            allowfullscreen='true'
            allowscriptaccess="always"
            wmode="opaque"
    ></embed> 
    </object>