Other - Confirm message not working in mac firefox

Confirm message not working in mac firefox

My code is

<input type="button" class="workButton" Style="Cursor:Hand" onclick="javascript:fnCloseProposal();" onMouseOver="this.T_FIX = [355,155];this.T_WIDTH=165;this.T_BGCOLOR='#FFFFE0';this.T_ BORDERCOLOR='#000000';this.T_STATIC=true;this.T_FO NTFACE='Arial';this.T_FONTCOLOR='#000000'; this.T_TEMP=15000;return escape('Cancel emailing of this proposal.')" value ="Close" id="docancel">

when i click close button below function will fire


function fnCloseProposal()
{
if( confirm( 'Do U want to quit ))
{

window.close();
}

}

confirm will appear with Ok And Cancel

if i click Ok rest of the code is not working .

please help me what to do

problem only in mac