Safari does not have an “allowed sites” function. To enable popups only for certain websites in Safari, you will have to turn off the pop-up blocker while on the site and turn it on again when leaving the site.
Safari on Mac OS X
Open Safari and select Preferences from the Safari menu.
Enable pop-up windows by unchecking the box “Block pop-up windows”.
Safari on iOS (iPhone, iPad)
From the home screen go to “Settings”;
then scroll down to “Safari” and tap to open;
and then scroll down to “Block Pop-ups” and turn it off.