Curious difference in behavior between Chrome & Safari extensions w/iFrames

Curious difference in behavior between Chrome & Safari extensions w/iFrames

I've developed extensions in Chrome and Safari, and I've noticed curious
differences in behavior in regards to iFrames. The extension I've
developed injects content scripts into all sites matching the url pattern:
http://*.nationstates.net/*
On Safari, this extension inject the content scripts into each iFrame
whose src also matches this pattern. On Chrome, it only injects the
content scripts into each web page that matches, never an iFrame.
The extension code is on Github.
Install Extension for Yourself:
http://forum.nationstates.net/viewtopic.php?f=15&t=243404
The easiest place to see this behavior is on here:
http://nationstatespostmaster.com/ Clicking an element opens an iFrame to
the nation page. On Chrome, the extension is not loaded. On Safari it is.