Compatibility Issue on Firefox for freetextbox to display on Cursor Location

Hi All

I am getting problem in putting text at the cursor location in freetext box which is place in a Place holder and .
My code is as follows:
 
                 First Name
        Last Name
        Email      
       
the statement
 "FTB_API['ctl00_ContentPlaceHolder1_ftbMailText'].InsertHtml
(ddlPlaceHolders.options[ddlPlaceHolders.selectedIndex].text);"
is working fine on Internet Explorer but its not working on firefox
Please help me

Thanks
wajans