http://www.historyandnews.co.uk/layout/ProfessionalCSS_en/javascript/confirm.js
You could edit this file in your favorite text editor and change the confirmation message
you could edit the contactuserform.thtml (in the profiles directory of the theme) and remove the onclick and onkeypress attribute in this line:
Text Formatted Code
<input type="submit" value="{lang_submit}" onclick="return postconfirm();" onkeypress="return postconfirm();" class="submit"{xhtml}>
Text Formatted Code
<input type="submit" value="{lang_submit}" class="submit"{xhtml}>