Reference two php files at once
<p>I noticed that on facebook, when you click on an image it opens up in their photo viewer. I understand that is done with javascript, but when you look at the url it says:</p>

<p><a href="http://www.facebook.com/photo.php?fbid=3230830261587&amp;set=a.1664092454121.85323.1591534315&amp;type=1&amp;theater" rel="nofollow">http://www.facebook.com/photo.php?fbid=3230830261587&amp;set=a.1664092454121.85323.1591534315&amp;type=1&amp;theater</a></p>

<p>But, you can still see your profile/or news feed (wherever you were when you clicked on the image) behind the photo viewer. How? It appears (upon observation of the url) that you have been redirected to facebook.com/photo.php. Is that the case? And how are you redirected back to www.facebook.com/(previous).php when you close the viewer?</p>
