when the browser tries to download a php page, it is an indication that a php error is occurring. go ahead and save the file, and send it to us in a zip archive, the downloaded file might contain clues to the problem.
If you have made lots of modifications to the site, something may have gotten incorrectly written on the pp_confirm.php page, try replacing it with an original unmodified copy from the power store download to see if that fixes the problem.
as for the google toolbar, i have no idea, send a link to your site so I can investigate.