i think Rick has this as a fix in 7.3.1, but for a quickie --

/scripts/download.inc.php

find:
PHP Code
 // Display inline
	if (preg_match("#(gif|jpg|png|txt)#",$file_extension)) {
		header("Pragma: public"); // required
		header("Expires: 0");
		header("Cache-Control: must-revalidate, post-check=0, pre-check=0");
		header("Cache-Control: private", false); // required for certain browsers
		header("Location:  {$config['ATTACHMENTS_URL']}/$file");
	} else {
		header("Content-Type: application/octet-stream");					  
		header("Content-Disposition: attachment; filename=\"$file_orig\";");   
		header("Content-Length: ".filesize("{$config['ATTACHMENTS_PATH']}/$file")); 
		readfile("{$config['ATTACHMENTS_PATH']}/$file");					   
	}

change to:
PHP Code

		header("Pragma: public"); // required
		header("Expires: 0");
		header("Cache-Control: must-revalidate, post-check=0, pre-check=0");
		header("Cache-Control: private", false); // required for certain browsers
		header("Location:  {$config['ATTACHMENTS_URL']}/$file");