Mac popup happy?

Could anybody point me in the right general direction for why Mac OS X Safari and Firefox would open up a new window/tab for this link? <a href="http://complaintsdevbrowse.hostedlabs.com/redirect_by_entry_id.php?entry_id=146802">FW: VitalChek Order Confirmation</a> It's password-protected to keep Google out until we launch, but I could send you a login offline, if you really want... Here is the actual HTTP exchange captured by LiveHTTPHeaders in Firefox on Windows: http://complaintsdevbrowse.hostedlabs.com/redirect_by_entry_id.php?entry_id=146802 GET /redirect_by_entry_id.php?entry_id=146802 HTTP/1.1 Host: complaintsdevbrowse.hostedlabs.com User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.8.1.4) Gecko/20070515 Firefox/2.0.0.4 Accept: text/xml,application/xml,application/xhtml+xml,text/html;q=0.9,text/plain;q=0.8,image/png,*/*;q=0.5 Accept-Language: en-us,en;q=0.5 Accept-Encoding: gzip,deflate Accept-Charset: ISO-8859-1,utf-8;q=0.7,*;q=0.7 Keep-Alive: 300 Connection: keep-alive Referer: http://complaintsdevwww.hostedlabs.com/tagged/confirmation.htm Authorization: Basic bHluY2g6ZnJlZDAwNw== HTTP/1.x 302 Found Date: Wed, 11 Jul 2007 19:14:04 GMT Server: HTTPD Set-Cookie: complaints=72de46df781bc8b305a69dc11b580ff0; path=/; domain=hostedlabs.com; secure Expires: Thu, 19 Nov 1981 08:52:00 GMT Cache-Control: no-store, no-cache, must-revalidate, post-check=0, pre-check=0 Pragma: no-cache Location: http://complaintsdevwww.hostedlabs.com/2007/july/3/FW__VitalChek_Order_Confirmation_146802.htm Content-Encoding: gzip Vary: Accept-Encoding Keep-Alive: timeout=3, max=100 Connection: Keep-Alive Transfer-Encoding: chunked Content-Type: text/html; charset=UTF-8 The redirect script is about as simple as it gets: <?php set_include_path('/webapps/data/sagacity.com/complaints.com/includes'); require 'globals.inc'; $public = "/webapps/data/sagacity.com/complaints.com/static"; $entry_id = (int) $_GET['entry_id']; $pattern ="$public/*/*/*/*_$entry_id.htm"; $files = glob($pattern); if (is_array($files) && count($files) === 1){ $basename = substr($files[0], strlen($public)); error_log("about to redirect to $STATICURL$basename"); header("Location: $STATICURL$basename"); exit; } header("Location: http://complaints.com"); ?> In this instance, globals.inc is a rather large file that gets included solely to set $STATICURL to 'http://complaintsdevwww.hostedlabs.com' I'm just not seeing any rational explanation for why my boss' computer is doing popups in all this. Surely a re-direct to a different sub-domain doesn't make Mac OS X decide it's a Good Idea to do popups... Does it?... The sub-domains are needed as the 'www' sub-domain will be a world-wide distributed server-farm DCN static data setup, while the 'browse' one will be a different world-wide distributed server-farm of PHP application boxes... I realize this isn't a PHP question, really, but I don't know what kind of a question it *IS* to know where to start looking, and my keyword combinations to Google have only returned a LOT of results with no relevance to my actual issue, as you might imagine... :-) -- Some people have a "gift" link here. Know what I want? I want you to buy a CD from some indie artist. http://cdbaby.com/browse/from/lynch Yeah, I get a buck. So?