In Firefox, data:// URLs do not inherit charset from parent frame. This is important because of cases such as <iframe src="data:image/svg+xml,..."> - the URL should be decoded as UTF-8 for correct round-tripping. On Leopard, this is currently masked by <rdar://problem/5845875> -[NSURLResponse textEncoding] incorrectly reports us-ascii encoding for data: URLs. Yet, we can fix this for other operating systems.
@Anne & @Alexey - Is this still applicable?
FWIW, <rdar://problem/5845875> was fixed a long time ago. Other than that, I do not remember much about this, would need to investigate.
I cannot reproduce inheritance with this test case: data:text/html;charset=utf-8,%FF?%FF%3Ciframe%20src=%22data:text/html,%25FF?%25FF%22%3E In particular the inner document shows ÿs as expected (and the outer �s). Similar result here with a non-data: URL as top-level document: http://software.hixie.ch/utilities/js/live-dom-viewer/saved/12013 I'd be inclined to close this as CONFIGURATION CHANGED based on that.